BoilerFaultCodesYour boiler's internal computer has encountered a critical error and has locked itself out for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Safety state: control unit error
What causes this fault?
This fault occurs when the boiler's main control board suffers an internal electronic failure or loses communication with its sensors. It is often caused by a component on the circuit board burning out or a loose connection in the internal wiring loom preventing the computer from operating safely.
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 E04 — no call-out fees, no surprises.
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