3D on a Viessmann Vitotronic 200: Evaporator sensor 2: The air discharge temperature sensor is used for defrosting the evaporator
Short answer
On a Viessmann heat pump, 3D means: Evaporator sensor 2: The air discharge temperature sensor is used for defrosting the evaporator. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Evaporator sensor 2: The air discharge temperature sensor is used for defrosting the evaporator.
Part involved: Evaporator sensor 2.
When it shows: The air discharge temperature sensor is used for defrosting the evaporator.
Likely causes:
- Evaporator temperature sensor lead break, heat pump stage 2.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
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 resistance value (Pt500A) at the terminal of the EEV PCB (see "EEV PCB [2]"); replace sensor if required.
Who to ask for: Viessmann-trained heat pump installer/service engineer.
What you might notice
Sources
- Service instructions Vitotronic 200 WO1C (5790974 GB, 2023-09) – brine/water & split variants ↗ · 5790974 VSA00002 · page 71 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026