Your boiler has detected an unusual and rapid change in water temperature, causing it to shut down for safety reasons to prevent overheating.

Flow and return sensor anomaly detected. Sudden temperature change detected on the flow or return sensor.

What causes this fault?

This fault occurs when the boiler's internal sensors detect an impossibly fast rise or fall in temperature, suggesting that water isn't moving through the unit correctly. The most common reason is a circulation failure, often caused by a faulty pump or a blockage in the pipework that prevents heat from being carried away from the heat exchanger.