341 on a NIBE heat pump: Recurring safety defr.: Alarm from outdoor unit (safety defrost repeated) [other NIBE documents: Safety defrost 10 times in a row / 10 repeated defrostings according to the protection conditions]
Short answer
On a NIBE heat pump, 341 means: Recurring safety defr.: Alarm from outdoor unit (safety defrost repeated) [other NIBE documents: Safety defrost 10 times in a row / 10 repeated defrostings according to the protection conditions]. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manuals for this range word it in different ways:
- Recurring safety defr.: Alarm from outdoor unit (safety defrost repeated) [other NIBE documents: Safety defrost 10 times in a row / 10 repeated defrostings according to the protection conditions].
- Inverter alarm type III: Not used function (false alarm).
Part involved: evaporator defrost; inverter and compressor drive.
When it shows: Alarm from outdoor unit (safety defrost repeated); Safety defrost 10 times in a row; 10 repeated defrostings according to the protection conditions Not used function (false alarm).
Likely causes:
- F2120: Air flow through evaporator; strong wind against fan; fault in cooling circuit | F2120: Poor airflow, e.g. because of leaves, snow or ice | S2125: Poor airflow, e.g. because of leaves, snow or ice.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: no/unknown - Compressor blocked.
Manual reset: Reset from the controller alarm menu ('reset alarm' / 'Reset alarm and try again'); alarm recurs if the cause remains.
What you can check
- Read the alarm text and the 'info/action' help on the controller display (VVM/SMO or S-series smartguide). NIBE's manuals let the homeowner select 'reset alarm' ('Reset alarm and try again' on S-series); if the lamp returns to normal the alarm has cleared. If it comes back, do not keep resetting: select 'aid mode' ('Auxiliary operation' on S-series) if offered, so any electric additional heat keeps heat/hot water going, and contact your installer. Check the outdoor unit is not blocked by leaves, snow or ice and that nothing obstructs the airflow.
- Read the alarm text and the 'info/action' help on the controller display (VVM/SMO or S-series smartguide). NIBE's manuals let the homeowner select 'reset alarm' ('Reset alarm and try again' on S-series); if the lamp returns to normal the alarm has cleared. If it comes back, do not keep resetting: select 'aid mode' ('Auxiliary operation' on S-series) if offered, so any electric additional heat keeps heat/hot water going, and contact your installer. Check the heat pump and indoor unit breakers/RCD at the consumer unit are on; if one trips again, leave it off and call an engineer.
What the engineer will check
- Check system volume and flow during defrost, particle filter, circulation pump, evaporator airflow, evaporator/defrost sensors and refrigerant circuit. NIBE lists: Check whether the outdoor unit has iced up and check the sensor; see outdoor unit manual; Air flow through evaporator; strong wind against fan; fault in cooling circuit; Poor airflow, e.g. because of leaves, snow or ice.
- Check main and group fuses and cable connections, supply voltage under load, inverter terminal blocks, inverter mounting/cooling paste, compressor wiring and compressor.
Who to ask for: NIBE-trained heat pump installer (NIBE PRO / VIP); NIBE-trained heat pump engineer and/or qualified electrician.
Certification: None specific beyond competent heat pump installer; electrical work to BS 7671; Electrical work to BS 7671 by a competent electrician (notifiable work under Part P in England & Wales).
What you might notice
Sources
- TECHNICAL INFORMATION - ALARM LIST SMO 40 (TIF EN 2042-1, M12658EN) ↗ · TIF EN 2042-1 M12658EN · page 9 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026