0B on a Viessmann Vitotronic 200: Short circuit/lead break, secondary circuit flow temperature sensor in the appliance
Short answer
On a Viessmann heat pump, 0B means: Short circuit/lead break, secondary circuit flow temperature sensor in the appliance. The manual does not say whether the heat pump stops. 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:
- Short circuit/lead break, secondary circuit flow temperature sensor in the appliance.
- External unit: The external unit switches off. Heating with booster heaters (if installed).
Part involved: Short circuit/lead break, secondary circuit flow temperature sensor in the appliance; External unit.
When it shows: Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Both compressors OFF The external unit switches off. Heating with booster heaters (if installed).
Likely causes:
- Short circuit/lead break, secondary circuit flow temperature sensor in the appliance.
- Outside temperature outside the application limits: Central heating application limits:.
- 230 V appliances: – 15 °C to +35 °C.
- 400 V appliances: – 20 °C to +35 °C Central cooling application limits:.
- All equipment: +15 °C to +45 °C.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
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 outdoor unit (air source models) is not blocked by leaves, debris or snow.
What the engineer will check
- Check resistance value (NTC 10 k) Ω at sensor connection on the controller PCB: See "Controller PCB and EEV PCB [6] ".
- See Viessmann service instructions.
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 180 · Reviewed 23 September 2026
- Service instructions Vitotronic 200 WO1C (5790974 GB, 2023-09) – brine/water & split variants ↗ · 5790974 VSA00002 · page 64 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026