BoilerFaultCodesYour boiler has detected that the electrical wiring is connected backwards or there is a grounding issue, which is preventing it from starting for safety reasons.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Reversed Polarity / Transpose Live & Neutral Check Earth
What causes this fault?
This fault occurs when the boiler detects that the live and neutral electrical wires have been swapped, or there is a poor connection to the building's earth. It is often triggered after recent electrical work in the home or if a plug-in appliance is causing a back-feed into the circuit. The system refuses to ignite because it cannot safely verify the presence of a flame when the electrical polarity is incorrect.
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.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like Simultaneous Slow Flashing (2Hz) — no call-out fees, no surprises.
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