BoilerFaultCodesYour boiler is not receiving any electrical power, which is why the lights are off and it isn't working.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Mains On neon - if not illuminated check mains supply, fuses, and input wiring
What causes this fault?
This fault occurs when the boiler's control system detects a complete break in the electrical circuit required to run the unit. The most common reason is a blown fuse or a loose connection in the wiring, which prevents electricity from reaching the internal components. In some cases, a surge may have damaged the main circuit board, causing it to fail entirely.
DIY fix possible
Check if your home's main consumer unit (fuse box) has tripped.Ensure the boiler's isolation switch (usually a white switch near the boiler) is turned on.Check the fuse in the boiler's fused spur switch, replacing it with a 3-amp fuse 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 I3 — no call-out fees, no surprises.
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Ideal Classic SE9 RS 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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