Danfoss (heat pumps) · No longer sold new in the UK. 73 codes across 4 product families, each taken from the manufacturer’s manuals. Danfoss technical support ↗
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73 codes
| Code | Meaning | Stops? | Homeowner check? |
|---|---|---|---|
| 00 | Communication failure | Yes | Yes |
| 01 | Return water sensor (T9) failure | Partly | Yes |
| 02 | Supply water sensor (T8) failure | Partly | Yes |
| 03 | Water flow switch protection | Yes | Yes |
| 04 | Phase sequence error (only applies to 3-phase models) | Yes | Yes |
| 05 | Excessive temperature difference between supply and return water (>13°C) | Yes | Yes |
| 06 | Internal electrical heater overheat protection (>85°C) | Partly | Yes |
| 07 | Condenser overheat protection | Yes | Yes |
| 08 | Hot water tank sensor (T3) failure | Partly | Yes |
| 09 | Buffer tank sensor (T2) failure | Partly | Yes |
| 10 | High pressure protection | Yes | Yes |
| 11 | Low pressure protection | Yes | Yes |
| 12 | Supply water temperature too high | Yes | Yes |
| 13 | Supply water temperature too low (cooling mode only) | Yes | Yes |
| 14 | Return gas temperature sensor (T5) failure | Yes | Yes |
| 15 | Exhaust gas temperature sensor (T4) failure | Yes | Yes |
| 16 | Exhaust gas temperature overheat protection | Yes | Yes |
| 18 | Frost protection, step 2 (non-fault) | No | Yes |
| 19 | Frost protection, step 1 (non-fault) | No | Yes |
| 20 | Air temperature sensor (T1) failure | Partly | Yes |
| 21 | Heating coil sensor (T7) failure | Partly | Yes |
| 22 | Cooling coil sensor (T6) failure | Partly | Yes |
| 23 | Exceeded operation range warning (non-fault) | No | Yes |
| alarm-brine-pump | The brine pump's integrated alarm has deployed (Opti models only) - pump air-locked or jammed; integrated shake function tries up to 5 times before alarming. | Yes | Yes |
| alarm-circulation-pump | The circulation pump's integrated alarm has deployed (Opti models only) - pump air-locked or jammed; shake function tries up to 5 times. | Yes | Yes |
| aux-heater | Overheating protection deployed. No auxiliary heater. | Partly | Yes |
| brine-out | Brine out is less than the set minimum temperature. Compressor stopped. No hot water production. | Yes | Yes |
| brineflow-low | Flow sensor not active during last start. Compressor stopped. No hot water production. | Yes | Yes |
| buffer-tank-sensor | Sensor fault alternatively cable fault. | Partly | Yes |
| com-error-expansion-card | Communication broken between display card and expansion card (indoor). | Partly | Yes |
| com-error-exv-card | Communication broken between display card and expansion valve control card (outdoor). | Yes | Yes |
| com-error-hp-card | Communication broken between display card and heat pump card (outdoor). | Yes | Yes |
| com-error-hub-card | Communication broken between display card and hub card (indoor). | Yes | Yes |
| defrost-sensor | Sensor fault alternatively cable fault. Defrost sensor. | Partly | Yes |
| discharge-pipe-sensor | Sensor fault alternatively cable fault. | Partly | Yes |
| distr-cir-1-sensor | Sensor fault alternatively cable fault. | Partly | Yes |
| distr-cir-2-sensor | Sensor fault alternatively cable fault. | Partly | Yes |
| el-heater-error | The electrical heater overheating protection has deployed. | Partly | Yes |
| err-phase-seq | Alarm that indicates that there is an incorrect phase sequence to the compressor. Only display and only the first 10 minutes. | Not stated | Yes |
| failsafe-mode | Sensor fault alternatively cable fault on one of the refrigerant sensors. The heat pump goes to failsafe mode and defrosts on time. | Partly | Yes |
| heat-pressure-error | The expected pressure and temperature change in the refrigerant circuit has not happened in the correct way at compressor start. | Yes | Yes |
| heating-circ-pump | Circulation pump is jammed. | Yes | Yes |
| heating-system-pump | Circulation pump is jammed. | Partly | Yes |
| hgw-sensor | Sensor fault alternatively cable fault. | Partly | Yes |
| high-pressure | Class A alarm. The heating circuit is the heat pump's high pressure circuit - check the circuit's level (pressure) and acknowledge. | Yes | Yes |
| high-pressure-error | High pressure switch has deployed. | Yes | Yes |
| high-return | Alarm that indicates that high return temperature prevents the compressor's operation. | Partly | Yes |
| high-return-line-temp | Return line temperature too high | Partly | Yes |
| hot-water-sensor | Sensor fault alternatively cable fault (the lower sensor, Start sensor). | Partly | Yes |
| hot-water-top | Sensor fault alternatively cable fault. | Partly | Yes |
| low-evap-temp-1 | Evaporation temperature too low. | Yes | Yes |
| low-evap-temp-2 | Too great a deviation in evaporation temperature average value. | Yes | Yes |
| low-heat-cir-flow | The flow sensor has registered too low a flow. | Yes | Yes |
| low-pressure | Class A alarm. The coolant (brine) circuit is the heat pump's low pressure circuit - check the circuit's level; contact a service technician if the alarm reoccurs. | Yes | Yes |
| low-pressure-error | Evaporation pressure has fallen too low. | Yes | Yes |
| low-pressure-transducer | Fault in low pressure transmitter alternatively cable fault. | Yes | Yes |
| low-return-temp-1 | The return line temperature is too low to start a defrosting. | Partly | Yes |
| low-return-temp-2 | The return line has fallen too low during defrosting. | Partly | Yes |
| max-temp-elec-hw | Too high temperature in heat pump junction box/electrical cabinet. | Not stated | Yes |
| motor-p-comp-error | The compressor motor protection has deployed. | Yes | Yes |
| motor-p-error | Deployed overload relay (overcurrent relay) for compressor or outdoor-unit fan; on certain models alarms from the brine pump or soft starter can also occur. Compressor stopped. | Yes | Yes |
| motor-p-fan-error | The fan motor protection has deployed. | Yes | Yes |
| no-of-tries-x-5 | Circulation pump is jammed. Start attempt made. | Partly | Yes |
| outdoor-sensor | Sensor fault alternatively cable fault. | Partly | Yes |
| pool-sensor | Sensor fault alternatively cable fault. | No | Yes |
| refr-1-sensor | Sensor fault alternatively cable fault. Refrigerant sensor 1 | Partly | Yes |
| refr-2-sensor | Sensor fault alternatively cable fault. Refrigerant sensor 2 | Partly | Yes |
| return-line-sensor | Sensor fault alternatively cable fault. Return line sensor. | Partly | Yes |
| room-sensor | Sensor fault alternatively cable fault. | No | Yes |
| sensor-cooling | Sensor fault. Cooling function stops. | Partly | Yes |
| suction-temp-sensor | Sensor fault alternatively cable fault. | Partly | Yes |
| supply-line-sensor | Sensor fault alternatively cable fault. Supply line sensor. | Varies by model | Yes |
| system-supply-line-sensor | Sensor fault alternatively cable fault. System supply line sensor. | Partly | Yes |