TO-T-VOR-NHZ-MFG on a Stiebel Eltron WPM 3 heat pump manager: The flow sensor of the electric emergency/booster heater in the multifunction assembly (MFG) is faulty/timeout
Short answer
On a Stiebel Eltron heat pump, TO-T-VOR-NHZ-MFG means: The flow sensor of the electric emergency/booster heater in the multifunction assembly (MFG) is faulty/timeout. 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: The flow sensor of the electric emergency/booster heater in the multifunction assembly (MFG) is faulty/timeout.
Part involved: multifunction assembly (MFG).
When it shows: The flow sensor of the electric emergency/booster heater in the multifunction assembly (MFG) is faulty/timeout.
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.
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