BoilerFaultCodesVaillant S.41 Fault Code
Also written as S41 — same fault.
The Vaillant S.41 fault code means: your boiler has detected that there is too much water in the system, causing the internal pressure to rise above safe operating levels.. It appears on 10 Vaillant models in our database.
Technical description: Water pressure too high. The system pressure is too high.
What causes the Vaillant S.41 fault?
This fault occurs when the water pressure inside your heating system exceeds the safe limit, often because the filling loop used to top up the system has been left slightly open or is leaking. It can also happen if the expansion vessel, which manages heat-related pressure changes, has failed or if the system has been significantly overfilled during recent maintenance.
This fault is more common in autumn when homeowners top up their system pressure ahead of the heating season and accidentally add too much water.
DIY fix possible
Check that the filling loop valves are fully closed and not leaking water into the systemBleed water from a radiator using a bleed key to reduce the system pressureMonitor the pressure gauge until it returns to the normal range (typically 1.0 to 1.5 bar)Restart the boiler to clear the status code
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Vaillant models that show the S.41 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT Pure 825 Repair: £80-150
- ecoFIT Pure 830 Repair: £80-150
- ecoFIT Pure 835 Repair: £80-150
- ecoTEC exclusive Repair: £0-120
- ecoTEC plus Repair: £80-150
- ecoTEC plus VU GB 656/4-5 A Repair: £80-150
- ecoTEC pro Repair: £80-200
- Home Combi 25 Repair: £90-180
- Home Combi 30 Repair: £90-180
- Home Combi 35 Repair: £90-180
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.
- Vaillant ecoFIT Pure 835 manual (PDF)
- Vaillant ecoTEC plus VU GB 656/4-5 A manual (PDF)
- Vaillant Home Combi 35 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026