35.S Low

Vaillant 35.S Fault Code

Also written as 35S — same fault.

The Vaillant 35.S fault code means: your boiler is currently running a routine internal check to ensure everything is operating correctly and is not displaying an active fault.. It appears on 1 Vaillant model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Status code check

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Vaillant models that show the 35.S fault code

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

Source

Vaillant 35.S 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 7 July 2026