A1-01 on a Daikin Altherma: EEPROM reading error
Short answer
On a Daikin heat pump, A1-01 means: EEPROM reading error. 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: EEPROM reading error.
Part involved: power supply / inverter electrical.
When it shows: Hydro PCB A1P detects EEPROM is abnormal.
Likely causes:
- Faulty hydro PCB A1P.
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: no.
Manual reset: Via power reset + via user interface.
What you can check
- Read the full error code and sub-code shown on the user interface (Malfunctioning screen; press the help button for Daikin's long description) 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
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
14 owner and engineer reports mention this.
- No heating on the Altherma: 7 reports
- Heat pump will not start on the Altherma: 5 reports
- Keeps stopping / cutting out on the Altherma: 2 reports
Sources
- Service manual Daikin Altherma Monobloc CA EBLQ/EDLQ05-07CAV3 (ESIE15-08B) ↗ · ESIE15-08B · page 22 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026