BoilerFaultCodesYour boiler has lost power completely and is unable to respond to any commands for heating or hot water because of an internal electrical failure.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: No mains Voltage supply. Fuse F1 or F2 blown. Transformer or connector failed. Board fault.
What causes this fault?
This fault occurs when the boiler's internal electrical circuit is broken, preventing power from reaching the main components. The most common reason is a blown protective fuse caused by an electrical surge or a faulty internal component, such as a failing pump or fan, which has overloaded the system. In some cases, the transformer or the main control board itself has failed, meaning the boiler can no longer process instructions.
DIY fix possible
Check if your main consumer unit (fuse box) has a tripped switchEnsure the fused spur switch next to the boiler is turned onCheck if the fuse in the external plug or spur has blown and replace if necessary
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like No lights and no functions (with demand) — no call-out fees, no surprises.
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Worcester Bosch 24si II is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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