L3 on a Daikin Altherma LT: Switch box temperature rise
Short answer
On a Daikin heat pump, L3 means: Switch box temperature rise. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Switch box temperature rise.
Part involved: inverter PCB thermal protection.
When it shows: With the compressor off, the radiation fin temperature is above 95°C. (Reset is made when the temperature drops below 80°C.) | With the compressor off, the radiation fin temperature is above 95°C. (Reset is made when the temperature drops below 80°C.) 3 3.
Likely causes:
- Fin temperature rise due to defective outdoor unit fan; Fin temperature rise due to short-circuit; Fin thermistor defective; Connector in poor contact; Outdoor unit PCB defective.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
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.
- Look at the outdoor unit from outside: check the air inlet/outlet and fan grille are not blocked by leaves, debris, snow or heavy ice build-up (do not remove panels or touch the fan).
What the engineer will check
- Follow the service-manual troubleshooting flow chart for this code: check fin temperature rise due to defective outdoor unit fan; check fin temperature rise due to short-circuit; check fin thermistor defective; check connector in poor contact; check outdoor unit PCB 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 ALTHERMA ERHQ006~008BAV3 / ERLQ006~008BAV3(9) / EKHBH(X)008BA (ESIE10-02) ↗ · ESIE10-02 · page 179 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026