TO-VOL-HK-MFG on a Stiebel Eltron WPM 3 heat pump manager: Incorrect communication with the MFG (heating circuit flow rate)
Short answer
On a Stiebel Eltron heat pump, TO-VOL-HK-MFG means: Incorrect communication with the MFG (heating circuit flow rate). 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: Incorrect communication with the MFG (heating circuit flow rate).
Part involved: multifunction assembly (MFG).
When it shows: Incorrect communication with the MFG (heating circuit flow rate).
Likely causes:
- Check the communication cable terminal or replace the communication cable.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
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.
- Check the heating system pressure gauge reading is in the normal range stated by your installer.
What the engineer will check
- Check the communication cable terminal or replace the communication cable.
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 53 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026