0A on a Viessmann Vitotronic 200: Short circuit/lead break, low pressure sensor
Short answer
On a Viessmann heat pump, 0A means: Short circuit/lead break, low pressure sensor. The heat pump stops until the fault clears or is reset. 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, low pressure sensor.
- Short circuit/lead break, low pressure sensor (suction gas pressure sensor).
- External unit: The external unit switches off.
Part involved: Short circuit/lead break, low pressure sensor; Short circuit/lead break, low pressure sensor (suction gas pressure sensor); External unit.
When it shows: Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Compressor OFF Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Both compressors OFF The external unit switches off.
Likely causes:
- Short circuit/lead break, low pressure sensor.
- Short circuit/lead break, low pressure sensor (suction gas pressure sensor).
- Number of registered events in the external unit has exceeded the message threshold.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
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
- Test voltage at the low pressure sensor connection: See "EEV PCB [2] ". 0.5 V: 0 bar.
- 4.5 V: Max. pressure, see sensor imprint.
- Check current at connection J10 (P1) of the EEV PCB: See "EEV PCB [4-3] / [4-4] ". Take refrigerant R410A into account.
- Check current at connection J10 (P1) of the EEV PCB: See "EEV PCB [4-6] / [4-7] ". Take refrigerant R410A into account.
- Check current at connection J10 (P1) on the EEV PCB: See "EEV PCB [4] ". Take refrigerant R410A into account.
- Test voltage at the low pressure sensor connection on the EEV PCB: See "controller PCB and EEV PCB [6] ". 0.5 V: 0 bar.
- Observe messages from the refrigerant circuit controller: "Diagnosis" "Refrigerant circuit" "Message statistics".
- Observe values displayed for the temperature and pressure sensors: "Diagnosis" "Refrigerant circuit" "External unit" Replace sensors if required.
- Check position of the DIP switch in the external unit.
Who to ask for: Viessmann-trained heat pump engineer with F-gas refrigeration certification.
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 157, 167, 173, 161, 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