All Daikin error codes
This page gathers Daikin error codes sorted by type of fault: what each code means, its likely causes, and what you can safely check before calling a professional.
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The Daikin codes on this page, grouped by type of fault.
power supply
circuit board
expansion valve
domestic hot water
circuit pressure
reversing valve
Temperature sensor — Daikin
These codes indicate a sensor that’s no longer returning a consistent value. The fault almost always comes from the sensor itself or its connector, rarely from the unit.
Code 80Medium severityair-to-water
Return water temperature sensor fault
Possible causes
- Faulty sensor
- Connector
Models affected: Altherma 3, Altherma LT, EHBH, EHVH
This fault requires a qualified technician. Do not open the unit.
Code 81Medium severityair-to-water
Outlet water temperature sensor fault
Possible causes
- Faulty sensor
- Sensor not properly fixed (81-04)
- Connector
Models affected: Altherma 3, Altherma LT, EHBH, EHVH
This fault requires a qualified technician. Do not open the unit.
Code E9023Informationair-to-water
EC sensor error — tDHW1 or DHW2 tank temperature sensor
Models affected: Altherma 3 ECH2O
Code E9024Informationair-to-water
Pressure sensor — S1NPH pressure sensor on the outdoor heat pump unit
Models affected: Altherma 3 ECH2O
Code E9025Informationair-to-water
Return temperature sensor error — R2T discharge temperature sensor on the outdoor heat pump unit
Models affected: Altherma 3 ECH2O
Code E9026Informationair-to-water
Suction pipe sensor error — R3T suction temperature sensor on the outdoor heat pump unit
Models affected: Altherma 3 ECH2O
Code E9027Informationair-to-water
Aircoil defrost sensor — R5T finned heat exchanger temperature sensor on the outdoor heat pump unit
Models affected: Altherma 3 ECH2O
Code E9028Informationair-to-water
Aircoil temp sensor — R4T finned heat exchanger temperature sensor on the outdoor heat pump unit (11-16 kW installations only)
Models affected: Altherma 3 ECH2O
Code E9029Informationair-to-water
FE cooling sensor error — R6T liquid-side temperature sensor on the outdoor heat pump unit
Models affected: Altherma 3 ECH2O
Code HCMedium severityair-to-water
Domestic hot water tank thermistor fault
Possible causes
- Faulty DHW tank sensor
- Sensor improperly positioned in the thermowell
- Faulty wiring
What you can check
- Check that the sensor is properly inserted in its housing
- Turn off power for 30 minutes, then restart
Models affected: Altherma 3, EHVH, EHBH, Altherma ECH2O
This fault requires a qualified technician. Do not open the unit.
Code P7Low severityair-to-air
Swing louver position sensor fault (louver motor)
Possible causes
- Faulty louver motor
- Louver stuck
- Position sensor failure
What you can check
- Check that the louver isn’t stuck
- Turn off power for 10 minutes, then restart
Models affected: FTXM, FTXA, FTXS
General fault — Daikin
These codes don’t point to a specific part: the unit is signaling that an internal safety feature has tripped.
Code 8HMedium severityair-to-water
Outlet water temperature abnormally high
Possible causes
- Insufficient water flow
- Faulty outlet sensor
- Setpoint too high
- Mixing valve stuck
What you can check
- Check that the circuit isn’t partially closed
- Bleed air from the circuit
- Check the outlet temperature setpoint
Affected models: Altherma 3, Altherma LT, EHBH, EHVH
Code A0Critical severityair-to-air
External protection tripped (safety input)
Possible causes
- External safety input activated
- External thermostat tripped
- Faulty safety input wiring
What you can check
- Check the accessories connected to the safety input
- Cut power for 30 minutes, then restart
Affected models: FTXB, FTXM, FTXA, FTXF
This issue requires a qualified technician. Do not open the unit.
Code E88Informationair-to-water
Unable to write parameters to external Flash memory. ▪ Contact a technician. — RoCon BM2C board
Affected models: Altherma 3 ECH2O
This issue requires a qualified technician. Do not open the unit.
Code E9006Informationair-to-water
Outlet temperature tv, BH > 65 °C — Outlet temperature sensor tv, BH
Affected models: Altherma 3 ECH2O
Code E9010Informationair-to-water
The jumper on connector “X21A” on board A1P is missing. ▪ Plug in the jumper. — Jumper on board A1P
Affected models: Altherma 3 ECH2O
Code E9021Informationair-to-water
HPSSystem — High-pressure switch S1PH on the external heat pump
What you can check
- ▪ Faulty high-pressure switch S1PH. ▪ Faulty external heat pump mainboard. ▪ Wiring, poor contact. ▪ Check, replace
Affected models: Altherma 3 ECH2O
This issue requires a qualified technician. Do not open the unit.
Code UACritical severityair-to-water
Incorrect indoor module / outdoor unit pairing
Possible causes
- Incompatible power modules
- A module was replaced with an incompatible model
- Software configuration not performed
What you can check
- A technician needs to check the compatibility of the part references
Affected models: Altherma 3, EHBH, EHVH, ERLQ, EDLQ
This issue requires a qualified technician. Do not open the unit.
Code UACritical severityair-to-air
Incompatible indoor/outdoor unit combination
Possible causes
- Incorrect indoor/outdoor unit pairing
- Incomplete software update
- Replacement with an incompatible model
What you can check
- Check model compatibility in the Daikin documentation
Affected models: FTXM, FTXA, RXM, RXA
This issue requires a qualified technician. Do not open the unit.
Code UHMedium severityair-to-water
System addressing error (units not properly identified)
Possible causes
- Incorrect addressing after installation
- Board replaced without re-addressing
- Multiple units sharing the same address
What you can check
- A technician needs to re-address the system
Affected models: Altherma 3, ERLQ, EDLQ
This issue requires a qualified technician. Do not open the unit.
Communication — Daikin
The indoor and outdoor units are no longer communicating. This is often the connecting cable or a board, not the refrigerant circuit.
Code E91Informationair-to-water
Duplicate bus ID on a CAN module; set a unique data address. — Connected CAN modules
Affected models: Altherma 3 ECH2O
Code U4Medium severityair-to-water
Communication fault between the indoor module and the outdoor unit
Possible causes
- Connecting cable cut or loose
- Reversed polarity on the terminal block
- Interference on the communication line
- Faulty PCB on one of the two modules
What you can check
- Check that the connecting cable is tight at both ends
- Check that polarity is correct
- Cut power for 30 minutes, then restart
Affected models: Altherma 3, Altherma LT, EHBH, EHVH, ERLQ, EDLQ
Code U5Low severityair-to-air
Communication error between remote control and indoor unit
Possible causes
- Faulty remote control cable
- Faulty wired remote control
- Interference on the remote control line
What you can check
- Check the remote control wiring
- Try operating from the infrared remote control
- Restart the unit
Affected models: FTXB, FTXC, FTXF, FTXM, FTXA
Code U7Medium severityair-to-air
Transmission error between outdoor unit microprocessors (main/inverter) or between outdoor units
Possible causes
- Outdoor PCB
- Internal wiring
Affected models: FTXM, FTXA, RXM, RXYM
This fault requires a qualified technician. Do not open the unit.
Code U8Medium severityair-to-water
Transmission error between remote controls (main/sub)
Possible causes
- Main/sub setting
- Remote control wiring
Affected models: ERLQ, EDLQ, EPRA
This fault requires a qualified technician. Do not open the unit.
Low pressure — Daikin
The refrigerant circuit pressure is too low. This often indicates a lack of refrigerant, meaning a leak needs to be located.
Code E9031Informationair-to-water
If this error occurs <15 times, reliable operation of the indoor pump is still ensured. ▪ Sporadic message during the unit’s continuous self-monitoring. ▪ No further action needed. If the error occurs 15 times, it causes a lockout and the cause may be: ▪ Current mains overvoltage. ▪ Refrigerant compressor blocked or faulty. ▪ Faulty inverter board on the outdoor heat pump. ▪ Wiring, poor contact. ▪ Service valves not opened on the outdoor heat pump. ▪ Check, eliminate the cause, replace. ▪ Contact a technician if needed. — Electrical component overvoltages
Affected models: Altherma 3 ECH2O
This fault requires a qualified technician. Do not open the unit.
Code E9032Informationair-to-water
▪ Faulty refrigerant compressor. ▪ Faulty inverter board on the outdoor heat pump. ▪ Check, replace. ▪ Contact a technician if needed. — Electrical components
Affected models: Altherma 3 ECH2O
This fault requires a qualified technician. Do not open the unit.
Code U0Critical severityair-to-water
Refrigerant shortage (air-to-water heat pump)
Possible causes
- Refrigerant leak
- Incorrect charge at installation
- Closed service valve
What you can check
- Check the service valves
- Do not restart — leak likely
Affected models: EHBH, EHVH, ERLQ, EDLQ
This fault requires a qualified technician. Do not open the unit.
Code U3Critical severityair-to-air
Test run not performed / transmission error
Possible causes
- Commissioning test not performed
Affected models: RXB, RXM, RXA, RXYM
This fault requires a qualified technician. Do not open the unit.
Power module — Daikin
Code P4Medium severityair-to-air
Inverter heatsink thermistor fault
Possible causes
- Faulty heatsink thermistor sensor
- Insufficient cooling
- Faulty sensor wiring
What you can check
- Cut power for 30 minutes, then restart
Affected models: RXM, RXA, RXS
This fault requires a qualified technician. Do not open the unit.
Code P4Medium severityair-to-water
Inverter heatsink thermistor fault
Possible causes
- Faulty inverter heatsink sensor
- Power board failure
What you can check
- Cut power for 30 minutes, then restart
Affected models: Altherma 3, ERLQ, EPRA
This fault requires a qualified technician. Do not open the unit.
Power supply — Daikin
The supply voltage is abnormal or absent. Check the dedicated circuit breaker first.
Code E9047Informationair-to-water
Overvoltage
What you can check
- The system detects an overcurrent to the compressor > 20 A for > 2.5 seconds, 16 times in 5 minutes ▪ Check the compressor. ▪ Check the compressor’s connection and wiring. ▪ Check the operation of the expansion valve (liquid backflow). ▪ Check the refrigerant charge amount and check for leaks. ▪ Check the power transistor. ▪ Check the external inverter PCB. ▪ Check whether the current LED blinks at regular intervals. ▪ Check whether the correct replacement part has been installed. ▪ Check whether the external main board is receiving power. ▪ Check whether the power supply complies with requirements
- Check for frequency fluctuations
Affected models: Altherma 3 ECH2O
This fault requires a qualified technician. Do not open the unit.
Electronic board — Daikin
A control or power board is no longer responding. A full restart sometimes clears a false fault; otherwise, replacement is needed.
Code PJCritical severityair-to-water
Capacity setting error (power board)
Possible causes
- Board replaced without capacity configuration
- Capacity jumper incorrectly positioned
- Incorrect indoor/outdoor unit pairing
What you can check
- Technician visit required for reconfiguration
Affected models: Altherma 3, ERLQ, EDLQ, EPRA
This issue requires a qualified technician. Do not open the unit.
Expansion valve — Daikin
The electronic expansion valve no longer regulates refrigerant flow.
Code UFMedium severityair-to-air
System not configured / wiring-piping mismatch
Possible causes
- Wiring and piping swapped between units (multi-split)
- Shut-off valve closed
- Refrigerant shortage
Affected models: RXB, RXC, RXF, RXM, RXA, RXS
Domestic hot water — Daikin
The domestic hot water circuit is faulty: tank sensor, three-way valve, or backup heater.
Code 9AMedium severityair-to-water
Domestic hot water tank circuit fault
Possible causes
- Faulty DHW tank sensor
- Stuck 3-way valve
- Failed DHW backup heating element
What you can check
- Cut power for 30 minutes, then restart
Affected models: Altherma 3, EHVH, EHBH, Altherma ECH2O
This issue requires a qualified technician. Do not open the unit.
Circuit pressure — Daikin
Code W8007Informationair-to-water
Warning: water pressure has exceeded the maximum allowed value. ▪ Faulty membrane expansion tank or incorrectly set pre-charge pressure. • Check, replace. ▪ [Max Pressure] setting too low. • Adjust the setting if needed. If the setting is correct, • drain some water to reduce the system pressure. — Water pressure in the heating system is high
Affected models: Altherma 3 ECH2O
Reversing valve — Daikin
Code U1Critical severityair-to-water
Phase reversal or missing phase (three-phase power supply)
Possible causes
- Two phases swapped at connection
- A missing phase
- Blown phase fuse
- Partially tripped circuit breaker
What you can check
- Check the electrical panel and fuses
- Have an electrician check the phase order
Affected models: three-phase Altherma 3, three-phase ERLQ, three-phase EPRA
This issue requires a qualified technician. Do not open the unit.
All Daikin codes published on the site
This list updates automatically whenever a new guide is added.
Technical information provided for guidance only, based on manufacturer documentation and field feedback. It does not replace a diagnosis by a qualified professional. Found an error on this page? Report it.