Low
S.04 on Vaillant Thermocompact

Your boiler is operating normally and is currently in the process of heating up after successfully lighting the burner.

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.

What the manual says

Manufacturer manual

Burner ignited (heating operation)

From this model's manual
Verified against the Vaillant Turbomax Plus 824 828e installation & service manual, page 38.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This code appears when the boiler's internal controls successfully detect a flame and confirm that the burner has lit correctly. It is a standard status message indicating that the system is now actively burning gas to heat your water or radiators. You do not need to take any action because this shows the boiler is working exactly as it should.

DIY fix possible

This fault may be fixable without an engineer. Check your manual first.

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