ED on a Viessmann Vitotronic 200: Ventilation comm.: Ventilation unit is switched off. Note After the time "Delay, subs. failure ventilation 7D90", message "EF Modbus subscriber" appears automatically
Short answer
On a Viessmann heat pump, ED means: Ventilation comm.: Ventilation unit is switched off. Note After the time "Delay, subs. failure ventilation 7D90", message "EF Modbus subscriber" appears automatically. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Ventilation comm.: Ventilation unit is switched off. Note After the time "Delay, subs. failure ventilation 7D90", message "EF Modbus subscriber" appears automatically.
Part involved: Ventilation comm.
When it shows: Ventilation unit is switched off. Note After the time "Delay, subs. failure ventilation 7D90", message "EF Modbus subscriber" appears automatically.
Likely causes:
- The ventilation unit was switched off by a safety device, e.g. in the event of negative pressure in the room.
- Connection to the ventilation unit is faulty.
- The ventilation unit is faulty.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
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).
What the engineer will check
- Eliminate negative pressure in the room, e.g. by opening the window briefly.
- Check the connecting cable to the ventilation unit.
- Check the ventilation unit.
- Check the fuses on the ventilation unit. Replace fuse if required.
- Check the controller PCB on the ventilation unit. Replace PCB if required.
Who to ask for: Viessmann-trained heat pump installer/service engineer.
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 · page 109 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026