C9 on a Viessmann Vitotronic 200: Refrigerant circ (SHD): Compressor is switched off.; Central heating and DHW heating occurs with other heat sources enabled for this purpose, e.g. an external heat generator or instantaneous heating water …
Short answer
On a Viessmann heat pump, C9 means: Refrigerant circ (SHD): Compressor is switched off.; Central heating and DHW heating occurs with other heat sources enabled for this purpose, e.g. an external heat generator or instantaneous heating water …. 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: Refrigerant circ (SHD): Compressor is switched off.; Central heating and DHW heating occurs with other heat sources enabled for this purpose, e.g. an external heat generator or instantaneous heating water ….
Part involved: Refrigerant circ (SHD).
When it shows: Compressor is switched off.; Central heating and DHW heating occurs with other heat sources enabled for this purpose, e.g. an external heat generator or instantaneous heating water heater.; The operation with booster heaters depends on the setting "Operating status after ….
Likely causes:
- Refrigerant circuit fault:.
- Safety high pressure switch has responded.
- Fan faulty.
- Primary pump faulty.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Safety lockout |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: Not stated per code; Vitotronic messages remain until the cause is removed and are acknowledged with OK (6150133 p.82). Unremedied acknowledged faults are redisplayed the following day.
Manual reset: Acknowledge with OK on the programming unit (user level permitted per 5817913 p.56-57) after the cause is remedied.
What you can check
- 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.
- Check the outdoor unit (air source models) is not blocked by leaves, debris or snow.
What the engineer will check
- Check flow and return temperature sensors in primary and secondary circuits.
- Check primary and secondary circuits for pressure and flow rate: See message "A9 Heat pump".
- Have the heat pump checked by a refrigeration engineer.
- Check fan or primary pump. Check safety high pressure switch.
- Vitocal 100-S/111-S: The switching signal of the safety high pressure switch can be tested at connection "H_Press" on the main PCB of the outdoor unit ….
- Vitocal 200-A/200-S/222-A/222-S/300-G/333-G: The continuity of the safety high pressure switch can be tested at the inverter.
- Vitocal 200-A, type AWCI-AC 201.A, Vitocal 200-G/ 222-G, Vitocal 300-A, type AWO-AC 301.B: The switching signal of the safety high pressure switch can be checked ….
- Vitocal 300-A, type AWO 302.B: Connections XF4.1/XF4.2: See separate wiring diagram. Note After removing the fault, switch the heat pump first off and then on ….
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 · page 104 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026