BoilerFaultCodesYour boiler is struggling to start the fan when you turn on your hot water taps, meaning the system cannot safely clear exhaust gases to begin heating.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: DHW mode – fan start up error
What causes this fault?
This fault occurs when the boiler's main control board sends a signal to start the fan, but it fails to rotate or reach the required speed to safely vent exhaust gases. The most common reasons are a buildup of dirt causing the fan bearings to seize or an electrical failure within the fan's motor or the wiring connecting it to the boiler.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like S.21 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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