Medium Warning
S.46 on Vaillant ecoTEC Pro / ecoTEC Plus

Your boiler is struggling to keep a steady flame when it is running at its lowest power setting, causing it to operate in a restricted safety mode.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Comfort safety mode flame loss at minimum load

What causes this fault?

This fault happens when the boiler's internal sensors can no longer detect a stable flame while the unit is ticking over at its lowest power. It is usually caused by a worn-out spark probe that can't 'see' the flame anymore, or a gas valve that is no longer delivering the precise, tiny amount of fuel needed for low-level operation.

Engineer required

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

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Related fault codes

F.28View →F.29View →

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