S.21 Low
Your boiler is performing a routine initial check of its internal air fan before it attempts to ignite the burner.
Technical description: Fan running
DIY fix possible
No action is required as this is a normal status message, not a fault code.Wait a few minutes to see if the boiler moves on to the next stage of its operation.If the code stays on screen for a long time without the boiler firing, try resetting the boiler once.
Protect yourself from future repair bills
A boiler cover plan would cover faults like S.21 — no call-out fees, no surprises.
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