E5 on a Daikin heat pump: Compressor motor lock
Short answer
On a Daikin heat pump, E5 means: Compressor motor lock. 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: Compressor motor lock.
Part involved: compressor / inverter drive.
When it shows: This malfunction will be output when the inverter compressor motor does not start up even in forced startup mode.
Likely causes:
- Compressor lock; High differential pressure (0.5MPa or more); Incorrect UVW wiring; Faulty inverter PC board; Stop valve is left in closed; Compressor lock (liquid suction (oil shortage)); Stop valve is left in closed. Warning: CAPACITOR SHOCK HAZARD. The capac itors (top surfaces) can hold up to 220V. Use correct precautions when servicing.
On the Altherma LT (low temperature split)
The manual says: OL Activation (compressor overload).
Part involved: compressor / inverter drive.
When it shows: ■ If the compressor OL is activated twice, the system will be shut down. ■ The error counter will reset itself if this or any other error does not occur during the following 60-minute compressor running time (total time). * The operating temperature condition is not specified | If the compressor OL is activated twice, the system will be shut down. The error counter will reset itself if this or any other error does not occur during the following 60-minute compressor running time (total time). 3 3 * The operating temperature condition is not specified.
Likely causes:
- Refrigerant shortage; Four way valve malfunctioning; Outdoor unit PCB defective; Water mixed in the local piping; Electronic expansion valve defective; Stop valve defective.
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 compressor lock; check high differential pressure (0.5MPa or more); check incorrect UVW wiring; check faulty inverter PC board; check stop valve is left in closed; check compressor lock (liquid suction (oil shortage)).
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 refrigerant shortage; check four way valve malfunctioning; check outdoor unit PCB defective; check water mixed in the local piping; check electronic expansion valve defective; check stop valve defective.
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 Daikin ALTHERMA HT ERSQ/ERRQ 011-016 AA V1/Y1 + EKHBRD (ESIE09-08C) ↗ · ESIE09-08C · page 170 · Reviewed 23 September 2026
- Service Manual ALTHERMA ERHQ006~008BAV3 / ERLQ006~008BAV3(9) / EKHBH(X)008BA (ESIE10-02) ↗ · ESIE10-02 · page 159 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026