BoilerFaultCodesYour boiler is having trouble switching between heating your radiators and providing hot water because a mechanical motor inside has stuck or failed.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Stepper motor fault (Diverter valve)
What causes this fault?
This fault occurs when the motor that controls your boiler's internal flow valve becomes jammed or suffers an electrical failure. The most common reason is that small bits of debris or sludge from the heating system have physically blocked the valve, putting too much strain on the motor and causing it to fail.
This issue is often noticed in autumn when the heating is turned on for the first time after summer, as the valve may have seized in the hot-water-only position due to lack of movement.
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 F15 — no call-out fees, no surprises.
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