BoilerFaultCodesTechnical description
Overheat thermostat operated or faulty.
What causes this fault?
This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety sensor to shut the system down. The most common reasons are a pump failure preventing water from moving away from the burner or a blockage caused by internal limescale and sludge.
This issue often appears when the heating is first switched on in autumn, as the internal pump can seize up after being inactive during the summer 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.
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