BoilerFaultCodesYour boiler has effectively switched itself off because it has detected that it is getting too hot, preventing internal damage or unsafe temperatures.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Safety thermostat or flue gas limiter activated
What causes this fault?
This fault occurs when the internal temperature of the boiler rises above a safe threshold, triggering a safety shut-off to prevent the unit from melting or cracking. The most common reason is a lack of water flow, often caused by a failing pump or a blockage of sludge and debris trapped within the main heat exchanger. In some cases, it can simply be a faulty sensor incorrectly reporting that the boiler is too hot.
This fault is more common in autumn or winter when the heating is first turned on after a long summer break, as circulation pumps are prone to seizing during periods of inactivity.
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 E9 — no call-out fees, no surprises.
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