INV-N-BOARD-LOW-TEMP on a Stiebel Eltron WPM 3 heat pump manager: Minor inverter fault: Temperature sensor fault, internal switching circuit temperature below the permissible range
Short answer
On a Stiebel Eltron heat pump, INV-N-BOARD-LOW-TEMP means: Minor inverter fault: Temperature sensor fault, internal switching circuit temperature below the permissible range. 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: Minor inverter fault: Temperature sensor fault, internal switching circuit temperature below the permissible range.
Part involved: compressor or fan inverter.
When it shows: Minor inverter fault: Temperature sensor fault, internal switching circuit temperature below the permissible range.
Likely causes:
- Inverter fault.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: yes - restarts after IWS fault time/idle time.
Manual reset: after 5 faults in 2 h run: IWS reset.
What you can check
- Read and note the full message code and time from the WPM display (DIAGNOSIS / NOTIFICATIONLIST if accessible without a code).
- Check the heat pump and controller circuit breakers/isolators at the consumer unit are on.
What the engineer will check
- Inverter fault.
Who to ask for: Heat pump service engineer (electrical/controls).
Certification: Qualified electrician competence for live-work on appliance electrics.
What you might notice
Sources
- OPERATION AND INSTALLATION Heat pump manager WPM 3 (DM0000035521) ↗ · A 316199-43934-9674 · page 48, 49 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026