B2 on a Viessmann Vitotronic 200: Fan motor speed monitor faulty
Short answer
On a Viessmann heat pump, B2 means: Fan motor speed monitor faulty. The heat pump keeps running. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 2 sources
What it means
The manuals for this range word it in different ways:
- Fan motor speed monitor faulty.
- KM BUS refrig. circ. 2: Refrigerant circuit controller activated;; Energy statement not calculated corlimited compressor operation. If this rectly (see chapter "Diagnosis energy operation is not possible, the compresstatement"). sor ….
Part involved: Fan motor speed monitor faulty; KM BUS refrig. circ. 2.
When it shows: Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Fan off, compressor remains in operation. Refrigerant circuit controller activated;; Energy statement not calculated corlimited compressor operation. If this rectly (see chapter "Diagnosis energy operation is not possible, the compresstatement"). sor shuts down after a few minutes. (cont.).
Likely causes:
- Fan motor speed monitor faulty.
- Communication fault with EEV controller (refrigerant circuit controller), heat pump stage 2 (if installed).
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Engineer needed? | Yes |
The heat pump keeps running.
Resetting itself: Not stated in 6150133.
Manual reset: Refrigerant circuit messages cannot be acknowledged in the message history (6150133 p.155); acknowledge the resulting 05/07/A9 message on the control unit.
What you can check
- This code is only visible to engineers in the service menu (Diagnosis > Refrigerant circuit > Message history); homeowners see message 05, 07 or A9 - note that code and call your contractor.
- Note the 2-character message code and message text shown on the Vitotronic 200 display (press OK for details) and give them to your heating contractor (operating instructions 5817913 p.56).
- You may acknowledge the message once with OK as described in the Vitotronic 200 operating instructions; if it reappears, do not keep acknowledging it - call your contractor.
- Check the heat pump breaker/isolator in the consumer unit is ON (do not repeatedly reset a breaker or RCD that keeps tripping).
- Check the heating system pressure gauge reading and report a low reading to your contractor; make sure the filling loop is closed.
What the engineer will check
- Check electrical connection of fan in.
- heat pump terminal area. Replace fan motor if necessary.
- If fault persists, notify a specialist.
- Check KM BUS connection. A fluctuating DC voltage of between approx. 20 V and 30 V can be measured at the KM BUS connection to ….
Who to ask for: Viessmann-trained heat pump engineer with F-gas refrigeration certification; Viessmann-trained heat pump installer/service engineer.
Certification: F-gas certificate (UK F-gas Regulations; Viessmann: refrigerant work by authorised refrigeration engineers only).
What you might notice
Sources
- Service instructions Vitotronic 200 type WO1C heat pump control unit (air/water split & monobloc, brine/water) (6150133, 2023-07) ↗ · 6150133 VSA00004 · page 165 · Reviewed 23 September 2026
- Service instructions Vitotronic 200 heat pump control unit (5692896, 2011-02) – 222-G/242-G/242-S/333-G/343-G/350-A ↗ · 5692896 VSA00001 · page 59-60 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026