L8-00 on a Daikin heat pump: Malfunction triggered by a thermal protection in the inverter PCB
Short answer
On a Daikin heat pump, L8-00 means: Malfunction triggered by a thermal protection in the inverter PCB. The heat pump stops until the fault clears or is reset. 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
The manual says: Malfunction triggered by a thermal protection in the inverter PCB.
Part involved: inverter PCB thermal protection.
When it shows: When compressor overload (except during start-up) is detected.
Likely causes:
- Closed stop valve in the refrigerant circuit.; Clogged refrigerant circuit.; Refrigerant overcharge or shortage.; Non‑condensables and/or humidity in the refrigerant circuit.; Faulty main PCB.; Faulty compressor or miswiring of the compressor power supply cable.
On the Altherma LT monobloc
The manual says: Electronic thermal overload.
Part involved: inverter PCB thermal protection.
When it shows: When compressor overload (except during startup) is detected.
Likely causes:
- Refrigerant circuit is clogged.; Refrigerant overcharge.; Faulty compressor.; Faulty outdoor inverter PCB.
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: Manual reset via user interface.
What you can check
On the Altherma
- 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.
- Do NOT bleed radiators while an error/malfunction symbol is displayed: Daikin operation manuals warn refrigerant may have leaked into the water circuit - ventilate and call your installer.
- If heating/hot water has stopped, the operation manual lets the user confirm on the Malfunctioning screen whether the backup/booster heater may take over as emergency heating (much higher running cost) until the installer attends.
On the Altherma LT monobloc
- 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
On the Altherma
- Check that all stop valves of the refrigerant circuit are open. . ; Check if the refrigerant circuit is clogged. . ; Check if the refrigerant circuit is correctly charged. . ; Check for the presence of non‑condensables and/or humidity in the refrigerant circuit. . ; Perform a check of the main PCB. . ; Perform a check of the compressor. .
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 monobloc
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
10 owner and engineer reports mention this.
- No heating on the Altherma: 7 reports
- Keeps stopping / cutting out on the Altherma: 2 reports
- No heating on the Altherma LT monobloc: 1 report
Sources
- Service manual Daikin Altherma 3 M EBLA/EDLA04~08E (ESIE22-09) ↗ · ESIE22-09 · page 65 · Reviewed 23 September 2026
- Service manual Daikin Altherma Monobloc CA EBLQ/EDLQ05-07CAV3 (ESIE15-08B) ↗ · ESIE15-08B · page 38 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026