36 on a Viessmann Vitotronic 200: Min. pressure differential between high and low pressure side exceeded before compressor start
Short answer
On a Viessmann heat pump, 36 means: Min. pressure differential between high and low pressure side exceeded before compressor start. The manual does not say whether the heat pump stops. 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:
- Min. pressure differential between high and low pressure side exceeded before compressor start.
- Hot gas temp sensor 1: Compressor 1 in a 2-stage refrigerant circuit is switched OFF.
Part involved: Min. pressure differential between high and low pressure side exceeded before compressor …; Hot gas temp sensor 1.
When it shows: Type "Note" (H) - triggers "07 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Compressor does not start. Compressor 1 in a 2-stage refrigerant circuit is switched OFF.
Likely causes:
- Min. pressure differential between high and low pressure side exceeded before compressor start.
- The stop limit for the hot gas temperature at compressor 1 is exceeded.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Severity | Warning |
| 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).
What the engineer will check
- Check high and low pressure sensors: See message codes "05" and "0A". Check secondary circuit flow rate.
- Check secondary pump. Ensure pressure compensation between the high pressure and low pressure sides. For this, switch the 4-way diverter valve with an "Actuator test".
- Check the compressor oil level. Top up with oil if required.
- Check if there is excess oil in the oil separator. Have the refrigerant circuit checked by a refrigeration engineer if necessary.
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 158, 89 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026