BoilerFaultCodesViessmann A5 Fault Code
The Viessmann A5 fault code means: your boiler has detected that the water pump is likely stuck or not moving water correctly, which means the system cannot heat up safely.. It appears on 12 Viessmann models in our database.
Technical description: N/A
What causes the Viessmann A5 fault?
This fault occurs when the boiler's control system detects that the internal pump is not rotating or circulating water effectively. The most common reason is that debris or magnetite from the heating system has jammed the pump's internal components, though it can also be caused by a mechanical failure of the motor or a communication error starting from the control board.
This issue is frequently seen at the start of autumn when heating is turned back on after being idle all summer, as stagnant debris is more likely to settle and seize the pump.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Viessmann models that show the A5 fault code
Click a model for the full fault code list and model-specific repair notes.
- A8 Repair: £120-£350
- Vitodens 050-W Repair: £180-450
- Vitodens 100-W / 200-W Repair: £180-450
- Vitodens 111-W Repair: £180-450
- Vitodens 200 Repair: £180-450
- Vitodens 200-W Repair: £180-450
- Vitodens 222-W Repair: £180-450
- Vitodens 333-F Repair: £180-450
- Vitola Biferral Repair: £0-120
- Vitopend 100 Repair: £180-350
- Vitopend 111 Repair: £0-120
- Vitorond 100 Repair: £180-450
Source
Viessmann A5 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