UF-00 on a Daikin heat pump: Reversed piping or bad communication wiring detection

What it means

On the Altherma

The manual says: Reversed piping or bad communication wiring detection.

Part involved: inter-unit communication / PCB combination.

When it shows: Reversed piping or bad communication, wiring detection.

Likely causes:

• Closed stop valve in the refrigerant circuit.; Piping and/or wiring mismatch.; If the unit has been powered off for a long time, lime might block the rotor of the pump. Use a Philips No. 2 screwdriver to push the deblocking screw of the rotor in (0.5 cm). Then turn the deblocking screw back and forth until the rotor is deblocked. (a) Note: Do NOT use excessive force. ( a ) If you cannot deblock the rotor of the pump with this method, you will need to disassemble the pump and turn the rotor by hand.

On the Altherma LT monobloc

The manual says: Communication error between hydro PCB A1P and outdoor main.

Part involved: inter-unit communication / PCB combination.

When it shows: When the interunit wiring between indoor and outdoor unit is incorrect or, when for 20 minutes during compressor operation: A: R2T R1T < 4°C, and B: R2T Te (or Tc during heating operation) > 14°C (24°C during heating operation).

Likely causes:

• Faulty wiring between indoor and outdoor unit.; Refrigerant shortage (incorrect charge / leakage).; Refrigerant circuit is clogged.

Is it safe?

On the Altherma

The heat pump stops until the fault clears or is reset.

Resetting itself: no.

Manual reset: Manual reset via user interface.

On the Altherma LT monobloc

The heat pump stops until the fault clears or is reset.

Resetting itself: unknown.

Manual reset: Auto-reset when problem is solved.

What you can check

On the Altherma

• Read the full error code and sub-code shown on the user interface (Malfunctioning screen; press the help button for Daikin's long description) and note it, with the date/time, for your installer.
• Do NOT bleed radiators while an error/malfunction symbol is displayed: Daikin operation manuals warn refrigerant may have leaked into the water circuit - ventilate and call your installer.
• If heating/hot water has stopped, the operation manual lets the user confirm on the Malfunctioning screen whether the backup/booster heater may take over as emergency heating (much higher running cost) until the installer attends.

On the Altherma LT monobloc

• Read the full error code and sub-code shown on the user interface (Malfunctioning screen; press the help button for Daikin's long description) and note it, with the date/time, for your installer.

What the engineer will check

On the Altherma

• Check that all stop valves of the refrigerant circuit are open. . ; Check that the piping and wiring connections of the system are correctly installed. and "7.2 Wiring diagram " [ 4 281 ] . ; | Troubleshooting 3.4 Symptom based troubleshooting 3.4.1 Symptom: Incorrect energy metering read-out Root cause category: hardware Possible failure Root cause Check Repair kWh values measured with field supplied meters show different values as the user interface. Backup heater wiring is NOT correct. Check backup heater wiring, see the installer reference guide. Adjust wiring if required. Values on user interface are incorrect, show strange values. User interface is replaced or reset to factory settings; Previous measurements are lost. Check if user interface is replaced or reset. Reset measurements of field supplied electrical meters and reset user interface and hydro PCB to factory settings. Values on user interface are incorrect, show strange values. Hydro PCB is replaced or reset to factory settings; Previous settings are lost. Check if hydro PCB is replaced or reset. Reset measurements of field supplied electrical meters and reset user interface and hydro PCB to factory settings. Unit operates in emergency mode. Backup heater is allowed in emergency mode, setting [4‑00]. Check setting. If you do NOT want the backup heater to run automatically in emergency mode, adjust setting. 3.4.2 Water pump related Symptom: Increased water pump sound level Root cause category: installation Possible failure Root cause Check Repair Water filter blocked. Dirty water. ▪ Check water filter, ▪ Check water quality. Clean the water filter. Air in the water circuit. NOT enough air purged. ▪ Check if all air purge valves are open, ▪ Check if air purge valves are installed on all highest points of the field installed water circuit. Purge air out of the unit and field supplied water system and backup heater. Water pressure too low. ▪ Water pressure NOT checked during filling, ▪ Air was purged from the water circuit after filling, ▪ Leakage. ▪ Expansion vessel is broken or not properly pre-adjusted. Check water pressure. Adjust water pressure if required (±2 bar). ; | Troubleshooting Possible failure Root cause Check Repair Water circuit partially blocked. Obstruction in the water circuit. Check water circuit for blockages. Remove possible blockages and check the water quality. Root cause category: component – mechanical Possible failure Root cause Check Repair Water pump mechanical problem. Internal pump friction. Check water pump. Replace water pump. Air purge blocked - air trapped in water circuit. Component failure. Check air purge valve. Replace air purge valve. Symptom: Incorrect water pump operation Root cause category: software control Possible failure Root cause Check Repair Unexpected water pump behaviour. Water pump software control. Water pump start/stop conditions: ▪ During space heating (cooling) or domestic hot water off: the pump is off, ▪ During space heating (cooling) or domestic hot water on: pump operation depends on setting [F‑0D] (continuous, sample or request). Remark: in domestic hot water operation the pump starts later than the compressor to avoid that the tank is cooled down by the cold water loop. Replace water pump. Root cause category: parameter (setting) Possible failure Root cause Check Repair Incorrect setting of pump operation mode (continuous, sample, request) (setting [F‑0D]). Incorrect setting. Confirm setting [F‑0]. Adapt setting [F‑0] if required (factory setting: [F‑0]=1). ; | Troubleshooting 3.4.3 Tap water related Symptom: High water pressure at tapping point Root cause category: component – mechanical Possible failure Root cause Check Repair Safety valve water side blocked. Component failure. Check safety valve. If required, replace safety valve. Field installed pressure reducing valve problem. ▪ Pressure reducing valve (to reduce pressure of the main water supply) NOT installed, ▪ Pressure reducing valve problem. Check water system pressure before and after the water pressure reducing valve. Install or replace water pressure reducing valve. Symptom: Tap water has white colour Root cause category: installation Possible failure Root cause Check Repair Extreme formation of anode residue. Water quality and composition of the water (chlorides, conductivity) can lead to accelerated reduction of the anode in the tank and aluminiumhydroxides will be formed on the bottom of the tank. (Remark: a NOT well controlled water softener can cause an increased amount of chlorides in the water.) Visual check for aluminiumhydroxide residue is ONLY possible with endoscope. ▪ Drain and flush the tank to remove the aluminiumhydroxides, ▪ Check correct setting of field supplied water softener (if installed). ; | Troubleshooting 3.4.4 Symptom: User interface is failure or frozen screen Root cause category: component – electrical Possible failure Root cause Check Repair Hydro PCB NOT operational. ▪ No power supply, ▪ Faulty transformer, ▪ PCB malfunction. ▪ Confirm if a small green led is blinking in regular intervals, ▪ Confirm power supply towards hydro PCB, ▪ Check good operation of transformer. ▪ Re-establish power to hydro PCB, ▪ Replace hydro PCB in case power supply and transformer are OK but led is NOT blinking. Reactor coil broken. Component problem. Check continuity of the reactor coil. Replace the reactor coil in case faulty. P1/P2 transmission cable broken/short-circuit. Check P1/P2 cable (16 V DC on BRC terminals and cable continuity). Repair P1/P2 cable if required. User interface failure. Check user interface software version. Update user interface software to the latest version. If problem persists, replace the user interface. No display. Display contrast too high or too low. Adjust contrast. Blocked screen. Mismatch between software and EEPROM on user interface. Power reset and user interface reset. 3.4.5 Symptom: Leak Root cause category: installation Possible failure Root cause Check Repair Drain connection of water safety valve leaking. Bad connection between unit drain pipe and field drain pipe. Check the drain connection of the water safety valve. Correct the drain connection if required. Drain of bottom drain plate NOT well connected. Bad connection of bottom drain plate and field drain connection. Check the drain connection between the bottom drain plate and the field drain. Correct the drain connection if required. Leakage of drain valve. Valve NOT completely closed. Check if drain valve is closed. Close the drain valve. Root cause category: component – mechanical Possible failure Root cause Check Repair Expansion vessel NOT pressurized. Component failure. Check expansion vessel. Replace expansion vessel. Safety valve blocked. Component failure. Check safety valve. Replace safety valve. Safety valve leaking. Component failure. Check safety valve. Replace safety valve. Leakage of drain valve. Component failure. Check drain valve. Replace drain valve. ; | Troubleshooting Possible failure Root cause Check Repair Domestic hot water tank leakage. Component failure. Check tank visually for leakages. Repair leakages. If NOT possible, complete unit has to be replaced. Air Purge leakage. Component failure. Check air purge valve for leakages. Replace air purge valve. 3.4.6 Symptom: Water flow or volume too low ; If this symptom is determined, check the steps in error codes 7H‑xx to solve the error. . 3.4.7 Compressor related Symptom: Compressor does not start Root cause category: software control Possible failure Root cause Check Repair Compressor does NOT start because water loop temperature is too low. Special software control activated - Water loop temperature is too low causing ONLY the backup heater to operate. Compressor will start when water temperature is high enough (for detailed water temperature values, see the operation range in the databook). Normal unit operation – no specific countermeasure required. — Compressor guard timer active. Compressor guard timer active. Once compressor has stopped it takes 180 seconds before it can restart. Normal unit operation – no specific countermeasure required. — Root cause category: component – electrical Possible failure Root cause Check Repair Power cables (U, V, W) incorrectly connected to compressor. Wrong assembly during repair. Confirm that the U, V, W wiring is correctly connected. for an indication how to connect correctly. Correct the U, V, W wiring. ; | Troubleshooting Symptom: Compressor does not increase frequency Root cause category: software control Possible failure Root cause Check Repair Compressor frequency limited - high discharge temperature protection function active. In case the discharge temperature is higher than 105°C the compressor frequency will be reduced. When the discharge temperature is lower than 105°C the frequency can increase again. Activation of the protection function can be caused by various reasons, therefore we recommend checking the following: ▪ Check refrigerant charge, ▪ Check expansion valve for correct operation, ▪ Check suction thermistor, ▪ Check discharge pipe thermistor. Based on the diagnosis execute one of the following actions: ▪ Correct the refrigerant charge, ▪ Replace expansion valve, ▪ Replace suction thermistor, ▪ Replace discharge pipe thermistor. Compressor frequency limited - high pressure protection function active. In case high pressure is higher than 38 bar the compressor frequency will be reduced. When the pressure drops below 36 bar the compressor frequency can increase again. Activation of the protection function can be caused by various reasons, therefore we recommend to check the following: ▪ Check refrigerant pressure sensor, ▪ Check high pressure side plate type heat exchanger for good water flow and heat exchange, ▪ Check the refrigerant charge. Based on the diagnosis execute one of the following actions: ▪ Replace refrigerant pressure sensor, ▪ Optimize the water flow through the high pressure side plate type heat exchanger, ▪ Correct the refrigerant charge. Compressor frequency limited. Inverter control active – target water leaving temperature (target sat. high pressure) reached. Check if saturated high pressure temperature is within range to heat up the water to the required temperature. — Compressor frequency limited - suction pipe superheat protection function active. This protection control activates when suction superheat is >10°C and expansion valve is fully open (480 pulse). Unit returns to normal operation when suction superheat is <4°C. Remark: check the suction superheat by measuring the suction temperature (with contact thermometer) before the compressor and comparing with the saturated evaporation temperature. Activation of the protection function can be caused by various reasons, therefore we recommend to check the following: ▪ Check refrigerant charge, ▪ Check expansion valve for correct operation, ▪ Check suction thermistor, ▪ Check the refrigerant circuit for blockages. Based on the diagnosis execute one of the following actions: ▪ Correct the refrigerant charge, ▪ Replace expansion valve, ▪ Replace suction thermistor, ▪ Remove detected blockages from the refrigerant circuit. ; | Troubleshooting Root cause category: installation Possible failure Root cause Check Repair PHE condenser (water side) (partial) blockage. Dirty water (particles). ▪ Check water flow rate registered by flow sensor, ▪ Check water side plate type heat exchanger for blockage. ▪ If required replace the water plate type heat exchanger, ▪ Check the water quality. Root cause category: component – mechanical Possible failure Root cause Check Repair Limited heat exchange between refrigerant loop and heat sink inverter could result in high inverter temperatures and limited compressor frequency. ▪ Bad contact between refrigerant loop and inverter heat sink, ▪ Lack of refrigerant. Check contact between refrigerant loop and PCB heat sink. — Root cause category: component – electrical Possible failure Root cause Check Repair Discharge pipe thermistor – higher temperature measured than actual. Deviation of thermistor (higher temperature measured than actual). Check discharge pipe thermistor. Replace discharge pipe thermistor or main PCB. Heat sink inverter thermistor - deviation. Deviation of thermistor (higher temperature measured than actual). ▪ Check heat sink inverter thermistor, ▪ Check PCB. ▪ Replace heat sink inverter thermistor, ▪ Replace PCB. Expansion valve incorrect control - superheat too high. ▪ Faulty suction thermistor, ▪ Faulty expansion valve control. ▪ Check suction thermistor, ▪ Check the expansion valve. ▪ Replace suction thermistor, ▪ Replace expansion valve. Symptom: Increased compressor sound level Root cause category: component – mechanical Possible failure Root cause Check Repair Compressor increased bearing friction/bearing failure. ▪ Bad lubrication of compressor internal rotating parts, ▪ Compressor at end of lifetime. No checks possible. Replace compressor. Unit produces (loud) noise or shakes. ▪ Refrigerant overcharge, ▪ Mixing of air in refrigerant system, ▪ Refrigerant undercharge. Check refrigerant. After vacuum drying, charge correct amount of refrigerant. ; | Troubleshooting Root cause category: component – electrical Possible failure Root cause Check Repair Expansion valve incorrect control - superheat too low. ▪ Faulty suction thermistor, ▪ Faulty expansion valve control. ▪ Check suction thermistor, ▪ Check the expansion valve. ▪ Replace thermistor when required, ▪ Replace expansion valve when required. 3.4.8 Symptom: Abnormal presence of ice Possible failure Root cause Check Repair General ice build-up. — — Outdoor unit installation MUST be protected from weather (wind, snow, ...). See installer reference guide for correct installation. Ice build-up on the outdoor unit. ▪ Clogged drain holes, ▪ Snow on the outdoor unit, ▪ Ice building up on the casing. Ice is NOT in direct contact with fins. ▪ Unclog drain holes or remove any scraps that can be used for ice to build up, ▪ Remove ice. Defrost operation malfunction. NOT enough defrost power: shortage of refrigerant. ▪ Check refrigerant charge, ▪ Check for leaks. ▪ Replace refrigerant, ▪ Fix leaks. Ice build-up at entry spot of refrigerant. Refrigerant shortage. ▪ Check refrigerant charge, ▪ Check for leaks. ▪ Replace refrigerant, ▪ Fix leaks. Partial ice up of coil. Partial refrigerant blockage. Check refrigerant circuit. Replace part where blockage occurs. Dirty coil. Check if coil is dirty. Clean coil. Bad weather conditions. Unit is NOT powerful enough to defrost due to too strong wind, snow, ... Outdoor unit installation MUST be protected from weather (wind, snow, ...). See installer reference guide for correct installation. ; | Troubleshooting 3.4.9 Symptom: Domestic hot water capacity shortage Root cause category: end user Possible failure Root cause Check Repair Too low domestic hot water setpoint. User set too low domestic hot water setpoint by schedule or manual operation. Check domestic hot water tank set temperature in combination with boiler volume and hot water usage. Adapt domestic hot water setpoint (e.g. 50~55°C). (Remark: check the weather dependent settings (relation outdoor temperature - setpoint) in case weather dependent control is activated.) Domestic hot water NOT activated. — Check if domestic hot water heating is activated. — Root cause category: parameter (setting) Possible failure Root cause Check Repair Setting domestic hot water operation mode [6‑0D] NOT set optimally. Setting domestic hot water operation mode [6‑0D] is set to 2 (scheduled ONLY). Check setting [6‑0D]. In case schedule is ONLY used, assure that the programmed schedule is in line with the timings hot water is required. Adapt the schedules if necessary. Root cause category: installation Possible failure Root cause Check Repair 3‑way valve does NOT switch correctly between space heating (cooling) connection and domestic hot water connection. 3‑way valve incorrectly mounted. Check the 3‑way valve. Correct the position of the 3‑way valve. Root cause category: component – electrical Possible failure Root cause Check Repair 3‑way valve blocked. Component failure. Check the 3‑way valve. Replace the 3‑way valve. Deviation of domestic hot water tank thermistor. Domestic hot water tank thermistor measures a higher temperature than actual (component failure). Check domestic hot water tank thermistor. Replace domestic hot water tank thermistor. ; | Troubleshooting 3.4.10 Symptom: General capacity shortage Root cause category: software control Possible failure Root cause Check Repair Compressor frequency limited - high discharge temperature protection function active. In case the discharge temperature is higher than 105°C the compressor frequency will be reduced. When the discharge temperature is lower than 105°C the frequency can increase again. Activation of the protection function can be caused by various reasons, therefore we recommend to check the following: ▪ Check refrigerant charge, ▪ Check expansion valve for correct operation, ▪ Check suction thermistor, ▪ Check discharge pipe thermistor. Based on the diagnosis execute one of the following actions: ▪ Correct the refrigerant charge, ▪ Replace expansion valve, ▪ Replace suction thermistor, ▪ Replace discharge pipe thermistor. Compressor frequency limited - high pressure protection function active. In case high pressure is higher than 38 bar the compressor frequency will be reduced. When the pressure drops below 36 bar the compressor frequency can increase again. Activation of the protection function can be caused by various reasons, therefore we recommend to check the following: ▪ Check refrigerant pressure sensor, ▪ Check high pressure side plate type heat exchanger for good water flow and heat exchange, ▪ Check the refrigerant charge. Based on the diagnosis execute one of the following actions: ▪ Replace refrigerant pressure sensor, ▪ Optimize the water flow through the high pressure side plate type heat exchanger, ▪ Correct the refrigerant charge. ▪ Compressor frequency limited, ▪ Suction pipe superheat protection function active. This protection control activates when suction superheat is >10°C and expansion valve is fully open (480 pulse). Unit returns to normal operation when suction superheat is <4°C. Remark: check the suction superheat by measuring the suction temperature (with contact thermometer) before the compressor and comparing with the saturated evaporation temperature. Activation of the protection function can be caused by various reasons, therefore we recommend to check the following: ▪ Check refrigerant charge, ▪ Check expansion valve for correct operation, ▪ Check suction thermistor, ▪ Check the refrigerant circuit for blockages. Based on the diagnosis execute one of the following actions: ▪ Correct the refrigerant charge, ▪ Replace expansion valve, ▪ Replace suction thermistor, ▪ Remove detected blockages from the refrigerant circuit. ; | Troubleshooting Root cause category: end user Possible failure Root cause Check Repair Space heating (cooling) or domestic hot water operation is NOT activated on the user interface. — Confirm if space heating (cooling) operation or domestic hot water operation is activated on user interface. Activate space heating (cooling) or domestic hot water operation on the user interface. Root cause category: parameter (setting) Possible failure Root cause Check Repair Displayed date/time is wrong - schedules NOT correctly executed. ▪ NOT set date/time after initial start-up, ▪ No power supply for more than 48 hours. Check date/setting and content of schedules. Set date/time according to operation manual instructions. Displayed date/time is wrong - schedules NOT correctly executed. Daylight Saving Time NOT set correctly. Check Daylight Saving Time settings. Set Daylight Saving Time according to operation manual. Schedules NOT activated. Schedules were NOT confirmed (see the schedule settings). Check schedules on the user interface. Set schedule according to user reference guide. Holiday setting active. Holiday setting is activated in the user interface. Check holiday settings. Set holiday settings correctly. Backup heater operation disabled. Setting backup heater operation mode [4‑00] is set to 0 (disable). Check setting [4‑00]. Change setting [4‑00] to 1. Second step of the backup heater is NOT allowed. Setting "enable backup heater step 2" [4‑07] is set to 0 (NOT allowed). Check setting [4‑07]. Change setting [4‑07] to 1. Backup heater equilibrium point was set too low. Setting "equilibrium temperature" [5‑01] was set too low. Check setting [5‑01]. Change setting [5‑01] to 0 or higher to more quickly allow backup heater operation. Root cause category: installation Possible failure Root cause Check Repair PHE condenser (partial) blockage. Dirty water (particles). ▪ Check water flow rate registered by flow sensor, ▪ Check plate heat exchanger for blockage. ▪ If required replace the plate heat exchanger, ▪ Check the water quality. 3‑way valve bypass between domestic hot water and space heating (cooling). 3‑way valve incorrectly mounted. Check the 3‑way valve. Correct the position of the 3‑way valve. Water filter blocked. Dirty water. ▪ Check water filter, ▪ Check water quality. ▪ Clean the water filter, ▪ Check the water quality. ; | Troubleshooting Possible failure Root cause Check Repair Air in the water circuit. NOT enough air purged. ▪ Check if all air purge valves are open, ▪ Check if air purge valves are installed on all highest points of the field installed water circuit. Purge air out of unit and field supplied water system and backup heater. Water circuit (partially) blocked. Dirty water. Check water circuit (unit + field) for blockages. Remove possible blockages and check the water quality. Root cause category: component – mechanical Possible failure Root cause Check Repair Refrigerant shortage. ▪ Refrigerant leakage, ▪ Incorrectly charged. ▪ Check refrigerant charge, ▪ Pressure test the system to check for leakage. If required, repair the leak and charge the correct refrigerant amount. Air Purge blocked - air trapped in water system. Component failure. Check air purge valve. Replace air purge valve. Root cause category: component – electrical Possible failure Root cause Check Repair Refrigerant pressure sensor - higher pressure measured than actual. Deviation of refrigerant pressure sensor (higher value measured than actual). Check refrigerant pressure sensor. Replace refrigerant pressure sensor. Discharge pipe thermistor – higher temperature measured than actual. Deviation of thermistor (higher temperature measured than actual). Check discharge pipe thermistor. Replace discharge pipe thermistor or replace PCB. Expansion valve incorrect control - superheat too high. ▪ Faulty suction thermistor, ▪ Faulty expansion valve control. ▪ Check suction thermistor, ▪ Check the expansion valve. Replace suction thermistor or replace expansion valve. Backup heater NOT working. Component failure. Check backup heater. Replace backup heater. Deviation of outlet water after backup heater thermistor will influence the backup heater control. ▪ Deviation of thermistor (higher temperature measured than actual), ▪ Bad contact between sensor and pipe. Check outlet water after backup heater thermistor. Replace outlet water after backup heater thermistor or PCB A1P. Flow sensor deviation – flow measured higher than actual. Component failure. Check the flow sensor. Replace the flow sensor. 3‑way valve blocked. Component failure. Check the 3‑way valve. Replace the 3‑way valve. ; | Troubleshooting 3.4.11 Symptom: Space heating (cooling) capacity shortage Root cause category: end user Possible failure Root cause Check Repair Space heating: too low leaving water temperature setpoint. Space cooling: too high leaving water temperature setpoint. User set too low (space heating) or too high (space cooling) leaving water temperature setpoint by schedule or manual operation. Check leaving water setpoint. Adapt leaving water setpoint. (Remark: check the weather dependent settings (relation outdoor temperature - setpoint) in case weather dependent control is activated.) Too low (space heating) or too high (space cooling) setpoint on room thermostat. User set too low (space heating) or too high (space cooling) room setpoint by schedule or manual operation. Check room thermostat setpoint. Adapt room thermostat setpoint. (Remark: check the weather dependent settings (relation outdoor temperature - setpoint) in case weather dependent control is activated.) Space heating (cooling) NOT activated. Check if space heating (cooling) is activated. Root cause category: parameter (setting) Possible failure Root cause Check Repair External room thermostat used with setting [C‑07] on value 2 (= RT control). Wrong setting of [C‑07] - unit control method. Check setting [C‑07]. Adjust setting to match application - see installer reference guide. Backup heater operation disabled (setting [4‑00] is set to 0 or 2). Setting backup heater operation mode [4‑00] is set 0 (backup heater disabled) or 2 (ONLY domestic hot water). Check setting [4‑00]. Change setting [4‑00] to 1. Setting domestic hot water operation mode [6‑0D] NOT set optimally. Setting domestic hot water operation mode [6‑0D] is set to 0 (reheat ONLY). This will cause the system to work too frequently in domestic hot water operation and less in space heating. Check setting [6‑0D]. It is advisable to set to factory setting (reheat + schedule) and program the schedule to heat the domestic hot water during periods of no space heating required. Root cause category: installation Possible failure Root cause Check Repair 3‑way valve does NOT switch correctly between space heating (cooling) connection and domestic hot water connection. 3‑way valve incorrectly mounted. Check the 3‑way valve. Correct the position of the 3‑way valve. ; | Troubleshooting Root cause category: component – electrical Possible failure Root cause Check Repair 3‑way valve blocked. Component failure. Check the 3‑way valve. Replace the 3‑way valve. Root cause category: system design Possible failure Root cause Check Repair Water circuit – requested capacity too high. Incorrect system selection. Check required capacity by heat load calculation. See the capacity tables in the engineering data book to know max. system capacity at indicated conditions. Adapt system design. Water circuit - water volume too big. ▪ Long water piping, ▪ Too many heating emitters. Check required capacity by heat load calculation. See the capacity tables in the engineering data book to know max. system capacity at indicated conditions. Adapt system design. Water circuit - pressure drop too big. ▪ Too small water piping, ▪ Too long water piping, ▪ Too many heating emitters. Compare the pressure drop of the total system with the water pump characteristics (See check of water pump). Decreased water flow will cause a drop in capacity. Adapt system design. 3.4.12 Symptom: Inaccurate temperature control Root cause category: parameter (setting) Possible failure Root cause Check Repair Incorrect setting of unit control method (setting [C‑07]). Incorrect setting of unit control method (setting [C‑07]) (leaving water control, room thermostat control, ext. room thermostat control). Check if setting [C‑07] (leaving water control, room thermostat control, ext. room thermostat control) is set according to the application. Adjust setting to match application. Incorrect setting of pump operation mode (continuous, sample, request) (setting [F‑0D]). Incorrect setting. Confirm setting [F‑0]. Adjust setting [F‑0] if required. (Factory setting: [F‑0]=1). Root cause category: installation Possible failure Root cause Check Repair User interface – thermostat sensor value NOT representing room temperature. Bad location of thermostat sensor (external influence) in case of room thermostat control (setting [C‑07]=2). Check if user interface is mounted in the correct position to measure the correct room temperature. Correct the position of the user interface for more accurate room temperature measurement. ; | Troubleshooting Root cause category: component – electrical Possible failure Root cause Check Repair Outlet water after backup heater thermistor deviation causes incorrect temperature control. ▪ Deviation of thermistor (lower temperature measured than actual), ▪ Bad contact between sensor and pipe. Check outlet water after backup heater thermistor. Replace outlet water after backup heater thermistor or hydro PCB. Deviation of domestic hot water tank thermistor. (Remark: ONLY valid for inaccurate domestic hot water temperature control.) ▪ Deviation of thermistor, ▪ Bad contact between sensor and pipe. Check domestic hot water tank thermistor. Replace domestic hot water tank thermistor or hydro PCB. User interface – thermostat sensor has incorrect reading of room temperature. Deviation of user interface room temperature sensor. Compare temperature measured by user interface with actual room temperature. In case of deviation the room temperature offset can be adjusted through setting [2‑0A]. FOR UNITS WITH BIZONE KIT INSTALLED: Possible failure Root cause Check Repair Outlet water mixed zone thermistor deviation causes incorrect temperature control of the mixed zone (low temperature). Deviation of thermistor (lower temperature measured than actual). ▪ Bad contact between sensor and pipe. Check outlet water mixed zone thermistor. Replace outlet water mixed zone thermistor or bizone PCB. 3‑way valve bypassing. 3‑way bypass valve jammed. check operation 3‑way mix valve. See component check 3‑way mixing valve. Insufficient water flow in the mixed zone. Bizone pump jammed. Check bizone pump. See component check bizone pump. Mixed circuit water filter clogged. Verify mixed zone water filter. Clean mixed zone water filter, see maintenance. 3.4.13 Symptom: Power consumption too high Root cause category: end user Possible failure Root cause Check Repair Too high domestic hot water setpoint. User set too high domestic hot water setpoint by schedule or manual operation. Check domestic hot water tank set temperature; avoid electric heater use. Adapt domestic hot water setpoint (e.g. 50~55°C). Too high leaving water temperature setpoint. User set too high leaving water temperature setpoint by schedule or manual operation. Check leaving water setpoint. Adapt leaving water setpoint (e.g. <55°C will reduce backup heater operation). ; | Troubleshooting Possible failure Root cause Check Repair Too high (space heating) or too low (space cooling) setpoint on room thermostat. User set too high (space heating) or too low (space cooling) room setpoint by schedule or manual operation. Check room thermostat setpoint. Adapt room thermostat setpoint. Root cause category: parameter (setting) Possible failure Root cause Check Repair Too high leaving water temperature (LWT) - weather dependent. Incorrect weather dependent setting --> too high LWT limit set [1‑00]~[1‑09]. Check leaving water temperature (LWT) high limit in weather dependent (setting [1‑03]). Adapt high leaving water temperature (LWT) limit for weather dependent heating (setting [1‑03]). User interface thermostat used with setting [C‑07] on value 1 (= external thermostat control). Wrong setting of [C‑07] - unit control method. Check setting [C‑07]. Adjust setting to match application - see installer reference guide. Pump keeps running all the time during space heating (cooling) operation. Wrong setting of [F‑0D] - pump operation. Check pump operation mode setting [F‑0D]. Change setting [F‑0D] from continuous operation (value 0) to Sample (1) or Request (2). See installer reference guide for applicable value. Setting disinfection operation day [2‑00] was set to 0 (each day). Setting disinfection operation day [2‑00] was set to 0 (each day). Check setting [2‑00]. Adjust setting if necessary. Unit is running in emergency operation and is using backup heater ONLY. [4‑06] is set to 1. Unit is running in emergency operation and is using backup heater ONLY. [4‑06] is set to 1. Check setting [4‑06]. Adjust setting if necessary. Backup heater equilibrium point was set too high. Setting "equilibrium temperature" [5‑01] was set too high. Check setting [5‑01]. Change setting [5‑01] to less quickly allow backup heater operation. Setting domestic hot water operation mode [6‑0D] NOT set optimally. Setting domestic hot water operation mode [6‑0D] is set to 0 (reheat ONLY). This will cause the system to work too frequently in domestic hot water operation and less in space heating. Check setting [6‑0D] in combination with the re- heat setpoint [6‑0C]. It is advisable to set to factory setting (reheat + schedule) and program the schedule to heat the domestic hot water during periods of no space heating required. ; | Troubleshooting Root cause category: component – electrical Possible failure Root cause Check Repair Deviation of outlet water after backup heater thermistor will influence the backup heater control. ▪ Deviation of outlet water after backup heater thermistor (lower temperature measured than actual), ▪ Bad contact between sensor and pipe. Check outlet water after backup heater thermistor. ▪ Replace outlet water after backup heater thermistor when required, ▪ Replace hydro PCB when required. Root cause category: system design Possible failure Root cause Check Repair Water circuit – requested capacity too high causing the system to run at full capacity. Incorrect system selection. Check required capacity by heat load calculation. See the capacity tables in the engineering data book to know max. system capacity at indicated conditions. Adapt system design. 3.4.14 Symptom: System does not start or operate Root cause category: software control Possible failure Root cause Check Repair Thermostat ON conditions for space heating (cooling) are NOT met. Thermostat ON conditions for space heating (cooling) are NOT met. Confirm thermostat on conditions depending on the unit control method (setting [C‑07]): ▪ Setting 1: external room thermostat indicates by contact when to start/ stop, ▪ Setting 2: room thermostat control => compare setpoint with room thermistor value. - Thermo on: room temperature = setpoint - (hysteresis/2), - Thermo off = room temperature + (hysteresis/2). For setting of hysteresis, see setting [9‑0C], ▪ Setting 3: outlet water temperature control => Thermo on: outlet water temperature = setpoint. Thermo off: outlet water temperature –1,5°C. Change setpoint if required. ; | Troubleshooting Possible failure Root cause Check Repair Thermostat ON conditions for domestic hot water operation are NOT met. Thermostat ON conditions for domestic hot water operation are NOT met. Confirm thermostat on conditions depending on the selected domestic hot water control type (setting [6‑0D]). Change setpoint if required. Out of operation range (ambient temperature above 35°C). Ambient temperature higher than 35°C. No action - unit CANNOT operate when ambient temperature is above 35°C. Root cause category: end user Possible failure Root cause Check Repair Space heating (cooling) or domestic hot water operation is NOT activated on the user interface. Confirm if space heating (cooling) operation or domestic hot water operation is activated on user interface. Activate space heating (cooling) or domestic hot water operation on the user interface. Root cause category: parameter (setting) Possible failure Root cause Check Repair Displayed date/time is wrong - schedules NOT correctly executed. ▪ NOT set date/time after initial start-up, ▪ No power supply for more than 48 hours. Set date/time according to operation manual instructions. Set date/time according to operation manual instructions. Displayed date/time is wrong - schedules NOT correctly executed. Daylight Saving Time NOT set correctly. Check Daylight Saving Time settings. Set Daylight Saving Time according to operation manual. Incorrect setting of unit control method (setting [C‑07]). Incorrect setting of unit control method (setting [C‑07]) (leaving water control, room thermostat control, ext. room thermostat control). Check if setting [C‑07] (leaving water control, room thermostat control, ext. room thermostat control) is in set according to the application. Incorrect setting of space heating OFF temperature (setting [4‑02]) or space cooling OFF temperature (setting [F‑01]). Incorrect setting of space heating OFF temperature (setting [4‑02]) or space cooling OFF temperature (setting [F‑01]). Check if setting space heating OFF temperature (setting [4‑02]) is correct (keep at 35°C) or check if setting space cooling OFF temperature (setting [F‑01]) is correct (keep at 10°C). Preferential kWh rate power supply settings and electrical connections do NOT match. Preferential kWh rate power supply settings and electrical connections do NOT match. Check preferential kWh rate power supply settings and electrical connections (see installer reference guide). ; | Troubleshooting Root cause category: component – electrical Possible failure Root cause Check Repair Hydro PCB NOT operational. ▪ No power supply, ▪ Faulty transformer, ▪ Hydro PCB malfunction. ▪ Confirm that HAP led is blinking in regular intervals, ▪ Confirm power supply towards hydro PCB, ▪ Check good operation of transformer. ▪ Re-establish power to hydro PCB. Replace hydro PCB in case power supply and transformer are OK but led is NOT blinking. Outdoor unit PCB malfunction (Main PCB, inverter PCB, …) ▪ No power supply, ▪ Outdoor unit PCB malfunction. ▪ Confirm that HAP led is blinking in regular intervals, ▪ Confirm power supply towards outdoor unit PCB, ▪ Check good operation of outdoor unit PCB. ▪ Re-establish power to outdoor unit PCB. Replace outdoor unit PCB in case power supply is OK but led is NOT blinking or in case of PCB not operating correctly. Reactor coil broken. Component problem. Check continuity of the reactor coil. Replace the reactor coil in case faulty. Root cause category: hardware Possible failure Root cause Check Repair Cooling/heating operation starts, but stops immediately. ▪ Refrigerant overcharge, ▪ Mixing of air in refrigerant system. Check refrigerant. After vacuum drying, charge correct amount of refrigerant. 3.4.15 Symptom: The pump is blocked ; | Components ; Components ; Turn ON the power of the unit. 2 Activate DHW operation via the user interface. ; Measure the voltage on connector X2M pin 13 and pin 14a. Result: The measured voltage MUST be 230 V AC. ; Measure the voltage on connector X2M pin 13 and pin 12. Result: The measured voltage MUST be 230 V AC. ; De-activate DHW operation and activate Space operation via the user interface. ; Measure the voltage on connector X2M pin 13 and pin 14a. Result: The measured voltage MUST be 230 V AC. ; Measure the voltage on connector X2M pin 13 and pin 12. Result: The measured voltage MUST be 0 V AC. ; | Components Are the measured voltages correct? Action Yes Perform a position check of the 3‑way valve (automatic procedure), see "4.1.1 Checking procedures " [ 4 99 ] . No Continue with the next step. ; Measure the voltage on connector X17A pin 5 and 7. Result: The measured voltage MUST be 230 V AC. Is the measured voltage on connector X17A correct? Action Yes Continue with the next step. No Perform a check of the hydro PCB, see "4.12.1 Checking procedures " [ 4 175 ] . ; Disconnect connector X20A from the hydro PCB. ; Activate DHW operation via the user interface. ; Measure the resistance between X20A pin 3 and 5. Result: The measured resistance MUST be 0 Ω. ; De-activate DHW operation and activate Space operation via the user interface. ; Measure the resistance between X20A pin 1 and 5. Result: The measured resistance MUST be 0 Ω. Is the resistance for both measurements on connector X20A correct? Action Yes Relay KVR is switching correctly. Correct the wiring between X20A, X17A and X2M, see "7.2 Wiring Diagram " [ 4 281 ] . No Relay KVR is NOT switching correctly. Replace the hydro PCB, see "4.12.2 Repair procedures " [ 4 178 ] , To perform a position check of the 3-way valve (automatic procedure) Prerequisite: First perform an electrical check of the 3‑way valve, see "4.1.1 Checking procedures " [ 4 99 ] . ; Turn ON the power of the unit. 2 Activate DHW operation via the user interface. ; Use a contact thermometer to measure the temperature at the 3‑way valve water inlet, the domestic hot water exit and the space heating exit. Exit Temperature Domestic hot water Same as the 3-way valve inlet Space heating "Much" lower than the 3-way valve inlet ; The 3-way valve can be installed in accordance with one of the following four configurations. Water inlet and exit locations differ depending on the configuration used in your unit.

Who to ask for: Heat pump installer (Daikin-trained).

Certification: None specific; MCS-certified installer recommended.

On the Altherma LT monobloc

Who to ask for: Heat pump installer (Daikin-trained).

Certification: None specific; MCS-certified installer recommended.

What you might notice

• Controller / thermostat problem
• No heating

What owners and engineers report

14 owner and engineer reports mention this.

• No heating on the Altherma: 7 reports
• Controller / thermostat problem on the Altherma: 6 reports
• No heating on the Altherma LT monobloc: 1 report

Sources

• Service manual Daikin Altherma 3 M EBLA/EDLA04~08E (ESIE22-09) ↗ · ESIE22-09 · page 79 · Reviewed 23 September 2026
• Service manual Daikin Altherma Monobloc CA EBLQ/EDLQ05-07CAV3 (ESIE15-08B) ↗ · ESIE15-08B · page 41 · Reviewed 23 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026