BoilerFaultCodesYour boiler has sensed that the water inside is getting much too hot and has shut down as a safety precaution.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: The heating flow thermistor is detecting a temperature in excess of 100°C.
What causes this fault?
This fault occurs when the water leaving the boiler reaches a dangerously high temperature, causing the system to shut down to prevent damage. The most common reasons are a pump failure that prevents water from moving through the system or a build-up of sludge and debris that blocks the main heat exchanger. It can also be caused by a faulty sensor that is incorrectly reporting the temperature to the control board.
This issue is more frequent during the first cold spell of autumn when the pump may struggle to start after being idle throughout the summer months.
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 18 — no call-out fees, no surprises.
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