Heat pumps · Error codes · Midea
P5Midea
P5 on a Midea heat pump: Big temperature difference between outlet water temperature and inlet water temperature
Short answer
On a Midea heat pump, P5 means: Big temperature difference between outlet water temperature and inlet water temperature. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 4 sources
What it means
On the M-Thermal Arctic HT R290 monobloc (MHC ...WD2N7)
The manual says: Big temperature difference between outlet water temperature and inlet water temperature.
Likely causes:
- See R290 service manual troubleshooting (section 6) for this code.
On the M-Thermal Mono R32 (MHC ...W/D2N8-B / -B2 'Arctic')
The manual says: High temperature difference between water side heat exchanger water inlet and water outlet temperatures protection.
Likely causes:
- Temperature sensor not connected properly or has malfunctioned.
- Water piping contains air.
- Insufficient water flow.
- Hydronic system main PCB damaged.
- Inverter module protection.
- DC bus low or high voltage protection.
- MCE error(DC bus low or high voltage protection or software over current protection).
- Zero speed protection.
- Excessive compressor frequency variation.
- Actual compressor frequency differs from target frequency.
- High pressure protection.
- PED board self checking fail.
- Contactor stuck or 908 self checking fail.
- Method 1: measure the resistance between any two of the 5 bridge rectifier terminals. If any of the resistances is close to zero, the bridge rectifier.
- Method 2: dial a multimeter to the diode setting:.
On the M-Thermal Mono R32 compact (MHC ...WD2N8-C, 5/7/9/12/14/16 kW)
The manual says: High temperature difference protection between water inlet and water outlet of the plate heat exchanger.
Likely causes:
- Valves not fully open.
- dirty filter.
- air in system.
- water pressure below 1 bar.
- pump speed too low.
- expansion vessel broken.
- circuit resistance too high.
On the M-Thermal Split R32 (MHA outdoor + HB hydronic box)
The manual says: High temperature difference between water side heat exchanger water inlet and outlet temperatures protection.
Likely causes:
- Temperature sensor not connected properly or has malfunctioned.
- Water piping contains air.
- Insufficient water flow.
- Hydronic box main PCB damaged.
- Inverter module protection.
- DC bus low or high voltage protection.
- MCE error(DC bus low or high voltage protection or software over current protection).
- Zero speed protection.
- Excessive compressor frequency variation.
- Actual compressor frequency differs from target frequency.
- High pressure protection.
- PED board self checking fail.
- Contactor stuck or 908 self checking fail.
- Method 1: measure the resistance between any two of the 5 bridge rectifier terminals. If any of the resistances is close to zero, the bridge rectifier.
- Method 2: dial a multimeter to the diode setting:.
Is it safe?
On the M-Thermal Arctic HT R290 monobloc (MHC ...WD2N7)
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
On the M-Thermal Mono R32 (MHC ...W/D2N8-B / -B2 'Arctic')
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
On the M-Thermal Mono R32 compact (MHC ...WD2N8-C, 5/7/9/12/14/16 kW)
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
On the M-Thermal Split R32 (MHA outdoor + HB hydronic box)
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
What you can check
- Read and note the exact code shown on the controller display.
- Check the heat pump's breaker/isolator at the consumer unit is on.
- Read the system pressure gauge and report the reading to your engineer (manuals ask for more than 1 bar when cold).
- Check the filling loop valves are closed.
- Restart once via the controller (OFF then ON) as the manual allows; if the code returns, call an engineer.
What the engineer will check
On the M-Thermal Arctic HT R290 monobloc (MHC ...WD2N7)
- See R290 service manual troubleshooting (section 6) for this code.
On the M-Thermal Mono R32 (MHC ...W/D2N8-B / -B2 'Arctic')
- Temperature sensor not connected properly or has malfunctioned.
- Water piping contains air.
- Insufficient water flow.
- Hydronic system main PCB damaged.
- Inverter module protection.
- DC bus low or high voltage protection.
- MCE error(DC bus low or high voltage protection or software over current protection).
- Zero speed protection.
- Excessive compressor frequency variation.
- Actual compressor frequency differs from target frequency.
- High pressure protection.
- PED board self checking fail.
- Contactor stuck or 908 self checking fail.
- Method 1: measure the resistance between any two of the 5 bridge rectifier terminals. If any of the resistances is close to zero, the bridge rectifier.
- Method 2: dial a multimeter to the diode setting:.
On the M-Thermal Mono R32 compact (MHC ...WD2N8-C, 5/7/9/12/14/16 kW)
- Valves not fully open.
- dirty filter.
- air in system.
- water pressure below 1 bar.
- pump speed too low.
- expansion vessel broken.
- circuit resistance too high.
On the M-Thermal Split R32 (MHA outdoor + HB hydronic box)
- Temperature sensor not connected properly or has malfunctioned.
- Water piping contains air.
- Insufficient water flow.
- Hydronic box main PCB damaged.
- Inverter module protection.
- DC bus low or high voltage protection.
- MCE error(DC bus low or high voltage protection or software over current protection).
- Zero speed protection.
- Excessive compressor frequency variation.
- Actual compressor frequency differs from target frequency.
- High pressure protection.
- PED board self checking fail.
- Contactor stuck or 908 self checking fail.
- Method 1: measure the resistance between any two of the 5 bridge rectifier terminals. If any of the resistances is close to zero, the bridge rectifier.
- Method 2: dial a multimeter to the diode setting:.
Sources
- R290 M thermal Arctic HT Series Service Manual ↗ · 2025-10-15 v5 (from file name) · page 92 · Reviewed 23 September 2026
- Midea M thermal Arctic Mono (4~16kW) Service Manual ↗ · not stated (MBT Confidential) · page 65 (table); 99 (troubleshooting) · Reviewed 23 September 2026
- M-thermal Mono ATW Heat Pump Installation and Owner's Manual (5/7/9/12/14/16 kW) ↗ · 16125300001699 V4.0 · page PDF 78 (printed 75) · Reviewed 23 September 2026
- M-Thermal A Series Split R32 Service Manual (Midea CAC, 202004) ↗ · 202004 (file v31) · page 51 (table); 82 (troubleshooting) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026