BoilerFaultCodesTechnical description
Safety thermostat (limit thermostat) activation
What causes this fault?
This fault occurs when the water inside the boiler exceeds a safe temperature, causing the safety limit thermostat to trip and shut everything down. The most common reasons are a pump failure preventing water from circulating or a buildup of limescale and sludge blocking the internal heat exchanger. It can also happen if there is trapped air in the system or if all your radiator valves are closed at once.
This fault is more common when the heating is first turned on after summer, as circulation pumps can seize up during long periods of inactivity.
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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