BoilerFaultCodesTechnical description
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What causes this fault?
This fault occurs when the water inside the heat exchanger reaches a dangerously high temperature, triggering a safety switch to cut the power. It is usually caused by a lack of water flow, often due to a failed internal pump or a blockage in the system preventing the heat from escaping. In some cases, the thermostat itself may have become faulty and is reporting an incorrect temperature reading.
This issue often surfaces during the first cold snap of autumn when the heating is turned on after being idle all summer, which can cause internal parts like the pump 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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