AF on a Viessmann Vitotronic 200: Cylinder primary pump: Inadequate change of temperature in the DHW cylinder
Short answer
On a Viessmann heat pump, AF means: Cylinder primary pump: Inadequate change of temperature in the DHW cylinder. 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: Cylinder primary pump: Inadequate change of temperature in the DHW cylinder.
Part involved: Cylinder primary pump.
When it shows: Inadequate change of temperature in the DHW cylinder.
Likely causes:
- Circulation pump for cylinder heating faulty.
- Cylinder loading system flow rate too low; cylinder loading pump or 2-way valve on cylinder loading system faulty.
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 heating system pressure gauge reading and report a low reading to your contractor; make sure the filling loop is closed.
What the engineer will check
- Measure the voltage at the following connections:.
- Vitocal 300-A: Connection 224.6, see "Expansion PCB".
- Other heat pumps: Connection 211.4, see "Main PCB". Check circulation pumps and 2-way valve are mechanically sound. If necessary replace circulation pumps and/or 2-way valve.
Who to ask for: Viessmann-trained heat pump installer/service engineer.
Sources
- Service instructions Vitotronic 200 type WO1C heat pump control unit (air/water split & monobloc, brine/water) (6150133, 2023-07) ↗ · 6150133 VSA00004 · page 101-102 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026