Your boiler has detected that the temperature is changing too quickly or slowly between the flow and return pipes, causing it to shut down to prevent damage.

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.