B0 on a Viessmann Vitotronic 200: Fan communication fault
Short answer
On a Viessmann heat pump, B0 means: Fan communication fault. The heat pump keeps running. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manuals for this range word it in different ways:
- Fan communication fault.
- Device recognition: Heat pumps with refrigerant circuit controller [7-1] : Heat pump starts. Refrigerant circuit runs with reduced efficiency.; Other heat pumps: The heat pump does not start.
Part involved: Fan communication fault; Device recognition.
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. Heat pumps with refrigerant circuit controller [7-1] : Heat pump starts. Refrigerant circuit runs with reduced efficiency.; Other heat pumps: The heat pump does not start.
Likely causes:
- Fan communication fault.
- Parameter "5030 Output compressor stage" is set incorrectly.
- Error in recognising appliance version, incorrect coding card or PCBs faulty Vitocal 300-A, type AWO-AC 301.B:.
- Cable harness for pressure sensor and fill level sensor in refrigerant collector faulty.
- Charge level sensor of refrigerant collector faulty.
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 plug at connection J19: See.
- "EEV PCB [4] ". Check luster terminals in the heat.
- pump terminal area if necessary.
- Correct setting for "5030 Output compressor stage".
- Check the coding card: See "Controller and sensor PCB". Replace the coding card if necessary.
- Check PCBs. Replace PCBs if required.
- Vitocal 100-S/111-S: Check the ID of the jumper (blue) on the main PCB of the outdoor unit: See chapter "Main PCB [7] / [7-1] ".
- Vitocal 200-A/200-S/222-A/222-S: Check the DIP switch on the EEV PCB of the outdoor unit: See chapter "EEV PCB [4-3] / [4-4] ".
- Vitocal 200-G/222-G/300-G/333-G: Check the DIP switch on the EEV PCB: See chapter "EEV PCB [4-6] / [4-7] ".
- Vitocal 300-A, type AWO-AC 301.B: Check cable harness and/or fill level sensor for refrigerant collector: See chapter "EEV PCB [4] ". Note After removing the ….
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 · pages 165, 102 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026