BoilerFaultCodesTechnical description
Overheat thermostat operated or faulty
What causes this fault?
This fault occurs when the internal temperature of the boiler rises above a safe limit, triggering a safety sensor to cut the power. The most common reasons are a failed pump that isn't moving water away from the heat exchanger quickly enough, or a buildup of limescale and sludge that restricts water flow.
This fault often appears during the first cold spell of autumn when the heating is turned back on after being idle all summer, which can cause internal pump components to seize.
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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