BoilerFaultCodesViessmann 25 Fault Code
The Viessmann 25 fault code means: your boiler is getting too hot too quickly and is shutting itself down to prevent damage.. It appears on 12 Viessmann models in our database.
Technical description: Boiler operates with high boiler water temperature
What causes the Viessmann 25 fault?
This fault occurs when water cannot travel through the boiler fast enough to carry heat away, causing the internal temperature to spike dangerously high. The most common reasons are a failed circulation pump that isn't pushing the water or a significant blockage within the pipework or heat exchanger. In some cases, it may simply be that the internal sensors have become faulty and are providing inaccurate heat readings to the control board.
This fault often appears when the heating is first turned on after summer, as the internal pump can seize up during long periods of inactivity.
DIY fix possible
Check that your radiator valves are fully openEnsure the central heating pump is runningCheck if the system water pressure is between 1.0 and 1.5 bar
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Viessmann models that show the 25 fault code
Click a model for the full fault code list and model-specific repair notes.
- A8 Repair: £120-350
- Vitodens 050-W Repair: £150-450
- Vitodens 100-W / 200-W Repair: £150-450
- Vitodens 111-W Repair: £150-450
- Vitodens 200 Repair: £150-450
- Vitodens 200-W Repair: £150-450
- Vitodens 222-W Repair: £150-450
- Vitodens 333-F Repair: £150-450
- Vitola Biferral Repair: £180-450
- Vitopend 100 Repair: £120-350
- Vitopend 111 Repair: £180-450
- Vitorond 100 Repair: £120-350
Source
Viessmann 25 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026