H6 on a Daikin Altherma LT: Compressor start up failure
Short answer
On a Daikin heat pump, H6 means: Compressor start up failure. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Compressor start up failure.
Part involved: compressor / inverter drive.
When it shows: ■ The compressor fails to start in about 15 seconds after the compressor run command signal is sent. ■ Clearing condition: Continuous run for about 5 minutes (normal) ■ The system will be shut down if the error occurs 8 times | The compressor fails to start in about 15 seconds after the compressor run command signal is sent. Clearing condition: Continuous run for about 5 minutes (normal) 3 3 The system will be shut down if the error occurs 8 times.
Likely causes:
- Compressor relay cable disconnected; Compressor itself defective; Outdoor unit PCB defective; Stop valve closed; Input voltage out of specification.
Is it safe?
| 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
- Follow the service-manual troubleshooting flow chart for this code: check compressor relay cable disconnected; check compressor itself defective; check outdoor unit PCB defective; check stop valve closed; check input voltage out of specification.
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.
What you might notice
What owners and engineers report
1 owner and engineer report mentions this.
- No heating on the Altherma LT (low temperature split): 1 report
Sources
- Service Manual ALTHERMA ERHQ006~008BAV3 / ERLQ006~008BAV3(9) / EKHBH(X)008BA (ESIE10-02) ↗ · ESIE10-02 · page 173 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026