BoilerFaultCodesTechnical description
Switching difference
What causes this fault?
This fault occurs when the boiler detects that water is not moving through the system correctly, leading to an unnatural temperature gap between the outgoing and incoming pipes. It is usually caused by a blockage in the heat exchanger or a failing pump that can no longer circulate the water fast enough to keep the internal components cool. In some cases, the sensors themselves may be faulty and providing inaccurate readings to the main control board.
This issue often surfaces in autumn when the heating is first turned on after summer, causing debris or sludge to shift and block narrowed pipework.
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.