B7 on a Viessmann Vitotronic 200: KM BUS external unit: Compressor external unit does not; Energy statement not calculated corstart. rectly (see chapter "Diagnosis energy statement"). (cont.)
Short answer
On a Viessmann heat pump, B7 means: KM BUS external unit: Compressor external unit does not; Energy statement not calculated corstart. rectly (see chapter "Diagnosis energy statement"). (cont.). 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 manual says: KM BUS external unit: Compressor external unit does not; Energy statement not calculated corstart. rectly (see chapter "Diagnosis energy statement"). (cont.).
Part involved: KM BUS external unit.
When it shows: Compressor external unit does not; Energy statement not calculated corstart. rectly (see chapter "Diagnosis energy statement"). (cont.).
Likely causes:
- Communication fault with refrigerant circuit controller, external unit.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
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
- Check KM BUS connection. A fluctuating DC voltage of between approx. 20 and 30 V must be present at:.
- Terminals X5.14 and X5.15 on controller and sensor PCB.
- Terminal P501 on AVI PCB. Check KM BUS connecting cables of both PCBs; check power supply to PCBs; replace PCBs if necessary.
Who to ask for: Viessmann-trained heat pump installer/service engineer.
Sources
- Service instructions Vitotronic 200 heat pump control unit (5692896, 2011-02) – 222-G/242-G/242-S/333-G/343-G/350-A ↗ · 5692896 VSA00001 · page 60-61 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026