BoilerFaultCodesTechnical description
Flow/return valves closed, Stuck pump, or the boiler has overheated.
What causes this fault?
This fault occurs when the internal temperature of the boiler rises too quickly or exceeds a safe limit, triggering a safety shut-off. It is usually caused by a physical blockage in the pipework, a mechanical failure of the pump, or air trapped within the heat exchanger that prevents heat from being carried away. Essentially, the water is not moving through the boiler fast enough to keep it cool.
This issue often surfaces when the heating is turned back on for the first time in autumn, as the pump can seize up after sitting idle 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.