0C on a Viessmann Vitotronic 200: External unit: No functional impairment
Short answer
On a Viessmann heat pump, 0C means: External unit: No functional impairment. The heat pump keeps running.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: External unit: No functional impairment.
Part involved: External unit.
When it shows: No functional impairment.
Likely causes:
- Information on operating status of the external unit, e.g. defrosting active.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Information only |
| Engineer needed? | No |
The heat pump keeps running.
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 outdoor unit (air source models) is not blocked by leaves, debris or snow.
What the engineer will check
- See Viessmann service instructions.
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).
Sources
- 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