Low Information
S.3 on Vaillant ecoTEC sustain

Your boiler is currently trying to light the flame to start provide heating or hot water, and this is a normal status message rather than a permanent error.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Ignition sequence

What causes this fault?

This code appears when the boiler's control system sends a signal to generate a spark and open the gas valve simultaneously. It is a natural part of the start-up process where the appliance attempts to establish a flame to satisfy a demand for heat. If the boiler stays on this code without firing, it usually means there is a temporary struggle to sense the flame or a delay in gas reaching the burner.

DIY fix possible

No action required; this is a normal operational status.Wait for the boiler to complete its start-up sequence.If the code persists for several minutes without the boiler firing, try a Reset.

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Related fault codes

F.28View →F.29View →S. 2View →S. 4View →

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