20171 on a Stiebel Eltron WPM heat pump manager / WPMsystem: High relevance communication objects have been incorrectly transferred repeatedly between the IWS and inverter (fan section)
Short answer
On a Stiebel Eltron heat pump, 20171 means: High relevance communication objects have been incorrectly transferred repeatedly between the IWS and inverter (fan section). 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 have been incorrectly transferred repeatedly between the IWS and inverter (fan section).
Part involved: compressor or fan inverter.
When it shows: High relevance communication objects have been incorrectly transferred repeatedly between the IWS and inverter (fan section).
Likely causes:
- Inverter fault. Check leads and the relevant plug-in connectors, and replace if faulty. Check the power supply to the inverter.
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 - heat pump restarts after idle time (~10-12 min); locks out after 5 faults in 2 h run.
Manual reset: after 5 faults in 2 h: IWS/WPM 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.
- Check the outdoor unit air intake/discharge is not blocked by leaves, snow or ice (air source units).
What the engineer will check
- Inverter fault. Check leads and the relevant plug-in connectors, and replace if faulty. Check the power supply to the inverter.
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
- WPM notification list (WPM V2.9) - multilingual; English section pp.15-26 (DOC-00081866) ↗ · WPM V2.9 · page 18 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026