L5 on a Daikin heat pump: Inverter compressor abnormal
Short answer
On a Daikin heat pump, L5 means: Inverter compressor abnormal. 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 · 2 sources
What it means
On the Altherma HT (high temperature split)
The manual says: Inverter compressor abnormal.
Part involved: compressor / inverter drive.
When it shows: When an excessive current flows in the power transistor. (Instantaneous overcurrent al so causes activation.).
Likely causes:
- Defect of compressor coil (disconnected, defective insulation); Compressor start-up malfunction (mechanical lock); Defect of inverter PC board (A2P); Overcurrent; Overcurrent immediate; Defect of inverter PC board [A4P (1 ø) or A5P (3ø)].
On the Altherma LT (low temperature split)
The manual says: Output over current (inverter PCB).
Part involved: power supply / inverter electrical.
When it shows: ■ A position signal error occurs while the compressor is running. ■ A speed error occurs while the compressor is running. ■ An output over-current input is fed from the output over-current detection circuit to the microcomputer. ■ The system will be shut down if the error occurs 16 times. ■ Clearing condition: Continuous run for about 5 minutes (normal) | A position signal error occurs while the compressor is running. A speed error occurs while the compressor is running. An output over-current input is fed from the output over-current detection circuit to the 3 3 microcomputer. The system will be shut down if the error occurs 16 times. Clearing condition: Continuous run for about 5 minutes (normal).
Likely causes:
- Over-current due to defective power transistor; Over-current due to wrong internal wiring; Over-current due to abnormal supply voltage; Over-current due to defective PCB; Error detection due to defective PCB; Over-current due to closed stop valve; Over-current due to compressor failure; Over-current due to poor installation condition.
Is it safe?
On the Altherma HT (high temperature split)
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: unknown.
On the Altherma LT (low temperature split)
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: unknown.
Manual reset: Reset via the remote controller (Inspection/Test button) after the cause is fixed; some codes need a manual reset of the remote-controller memory (service manual section 1.4).
What you can check
- Read the full error code shown on the user interface and note it, with the date/time, for your installer.
- Check the heat pump isolator switch(es) and the consumer-unit breaker/RCD for the heat pump are ON. If a breaker or RCD has tripped, do not keep resetting it - leave it and call an engineer.
What the engineer will check
On the Altherma HT (high temperature split)
- Follow the service-manual troubleshooting flow chart for this code: check defect of compressor coil (disconnected, defective insulation); check compressor start-up malfunction (mechanical lock); check defect of inverter PC board (A2P); check overcurrent; check overcurrent immediate; check defect of inverter PC board [A4P (1 ø) or A5P (3ø)].
Who to ask for: F-gas certified heat pump engineer with electrical competence.
Certification: UK F-gas certification if the refrigerant circuit is opened; electrical competence (BS 7671) for inverter/PCB work.
On the Altherma LT (low temperature split)
- Follow the service-manual troubleshooting flow chart for this code: check over-current due to defective power transistor; check over-current due to wrong internal wiring; check over-current due to abnormal supply voltage; check over-current due to defective PCB; check error detection due to defective PCB; check over-current due to closed stop valve.
Who to ask for: Heat pump engineer / qualified electrician.
Certification: Electrical competence to BS 7671 (Part P where applicable) for mains supply work.
What you might notice
What owners and engineers report
2 owner and engineer reports mention this.
- No heating on the Altherma LT (low temperature split): 1 report
- Heat pump will not start on the Altherma LT (low temperature split): 1 report
Sources
- Service Manual Daikin ALTHERMA HT ERSQ/ERRQ 011-016 AA V1/Y1 + EKHBRD (ESIE09-08C) ↗ · ESIE09-08C · page 196 · Reviewed 23 September 2026
- Service Manual ALTHERMA ERHQ006~008BAV3 / ERLQ006~008BAV3(9) / EKHBH(X)008BA (ESIE10-02) ↗ · ESIE10-02 · page 183 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026