S.41 Medium

Vaillant S.41 Fault Code

Also written as S41 — same fault.

The Vaillant S.41 fault code means: your boiler has too much water in the system, causing the pressure to rise to a level that is higher than recommended for safe operation.. It appears on 25 Vaillant models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Water pressure > 2.8 bar

What causes the Vaillant S.41 fault?

This fault occurs when the water pressure inside your system rises to an unsafe level, usually because the filling loop has been left slightly open or or is leaking water into the system. It can also happen if the internal expansion vessel, which manages water pressure as it heats up, has failed or lost its air charge. In some cases, a faulty plate heat exchanger may be allowing fresh mains water to leak into the central heating circuit.

Typical repair cost £80-160 (including labour)

DIY fix possible

Check that the filling loop valves are fully closedBleed a radiator from the top valve to release excess waterMonitor the pressure gauge until it returns to between 1.0 and 1.5 barReset the boiler if the code does not clear automatically

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Vaillant models that show the S.41 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant S.41 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026