BoilerFaultCodesWhat the manual says
Manufacturer manualOverheat thermostat (which cuts off the gas valve)
What causes this fault?
This fault occurs when the water inside the heat exchanger reaches an unsafe temperature, triggering a safety switch to cut the power. The most common reasons are a pump failure preventing water from circulating or a build-up of sludge and debris that blocks the flow of heat away from the burner.
This issue often surfaces when the heating is first turned on after summer, as the internal pump can seize up from lack of use during the warmer months.
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 20: no call-out fees, no surprise bills.
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