6D on a Viessmann Vitotronic 200: Central cooling: Secondary circuit flow temperature too low
Short answer
On a Viessmann heat pump, 6D means: Central cooling: Secondary circuit flow temperature too low. 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:
- Central cooling: Secondary circuit flow temperature too low.
- Room cooling: Secondary circuit flow temperature too low.
Part involved: Central cooling: Secondary circuit flow temperature too low; Room cooling: Secondary circuit flow temperature too low.
When it shows: Type "Note" (H) - triggers "07 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Compressor does not start.
Likely causes:
- Central cooling: Secondary circuit flow temperature too low.
- Room cooling: Secondary circuit flow temperature too low.
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.
What the engineer will check
- Check parameter settings for cooling ("71xx"), e.g. "Min. flow temperature cooling 7103".
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 169, 175 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026