Low Information
S.21 on Glow-worm Ultracom 35 Store

Your boiler is performing a routine start-up check by running its internal fan before 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.

Technical description

fan pre-run

What causes this fault?

This code is not actually a fault, but a normal status message showing that the boiler's fan is spinning up to clear the combustion chamber. It occurs every time the boiler prepares to heat your water or radiators to ensure the system is safe before the gas ignites. If the boiler stays on this code for a long time without firing up, it may indicate a struggle to reach the required air pressure.

DIY fix possible

Wait for up to 60 seconds for the sequence to completeCheck if the display changes to a heating or hot water symbolIf the code stays stuck for minutes, try a simple reset by pressing the 'Reset' button

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