Low
S.01 on Vaillant Thermocompact

Your boiler is currently preparing its internal fan to safely start the heating process.

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

Fan running (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 status occurs when the boiler begins its ignition sequence and initiates the fan to clear out the combustion chamber. It is a normal part of the start-up process and indicates that the control board is successfully communicating with the fan motor. If the display stays on this code for a long time, it may suggest the fan is struggling to reach the speed required to proceed to the next step.

DIY fix possible

Check if the room thermostat is turned up to signal for heatWait up to 2 minutes for the boiler to complete its pre-ignition safety checksEnsure there is power to the boiler and the display is active

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