BoilerFaultCodesWhat the manual says
Manufacturer manualFLUE GAS OVERHEAT
What causes this fault?
This fault occurs when the gases produced by the burner become too hot, triggering a safety sensor to prevent damage to the boiler or flue. The most common reasons are a build-up of debris or limescale inside the main heat exchanger or a failing pump that isn't moving water through the system fast enough to carry the heat away.
This issue is more frequent in winter when the boiler is working under maximum load for long periods, which puts additional strain on a struggling heat exchanger or pump.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Avoid the next call-out bill
A cover plan would handle faults like L9: no call-out fees, no surprise bills.
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