BoilerFaultCodesYour boiler is struggling because the electricity supply from the national grid or your home's wiring is unstable or at the wrong frequency.
This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.
Technical description: Faulty mains frequency – electric mains error
What causes this fault?
This fault occurs when the boiler's internal computer detects that the incoming electricity supply is fluctuating outside of the standard UK 50Hz frequency. The most common reason is an unstable power supply from the national grid or electrical noise caused by other faulty appliances in your home interfering with the boiler's delicate electronics.
This fault may be more common during severe winter storms when overhead power lines are damaged, leading to 'dirty' or inconsistent electricity supply to homes.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like F35 — no call-out fees, no surprises.
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