COMMUNICATION-IWS-INV-H on a Stiebel Eltron WPM 3 heat pump manager: High relevance communication objects repeatedly transferred incorrectly between IWS and inverter
Short answer
On a Stiebel Eltron heat pump, COMMUNICATION-IWS-INV-H means: High relevance communication objects repeatedly transferred incorrectly between IWS and inverter. 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: High relevance communication objects repeatedly transferred incorrectly between IWS and inverter.
Part involved: compressor or fan inverter.
When it shows: High relevance communication objects repeatedly transferred incorrectly between IWS and inverter.
Likely causes:
- Inverter fault. Check wiring and associated plug-in connectors; replace if faulty. Test inverter power supply.
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. Check wiring and associated plug-in connectors; replace if faulty. Test inverter power supply.
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 49, 52 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026