BoilerFaultCodesVaillant S.62 Fault Code
Also written as S62 — same fault.
The Vaillant S.62 fault code means: your boiler is struggling to burn gas correctly and efficiently, which can lead to it locking out to ensure safety.. It appears on 3 Vaillant models in our database.
Technical description: Adjust CO2. Set the CO2 content.
What causes the Vaillant S.62 fault?
This fault occurs when the boiler's sensors detect an incorrect mixture of gas and air during the combustion process, meaning the flame is not burning as it should. The most common reasons are a drifting gas valve that needs recalibration or worn-out spark electrodes that are struggling to ignite the gas cleanly. In some cases, it can be caused by a fault in the main control board failing to manage the gas flow accurately.
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 →Vaillant models that show the S.62 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant S.62 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