Your boiler has shut down because there is a confusing difference between the temperatures recorded at its internal sensors, often caused by poor water flow or a sensors reading incorrectly.

Different temperature error

What causes this fault?

This fault occurs when the boiler's control system detects a significant conflict between the readings of the flow and return temperature sensors. The most common cause is poor water circulation through the heat exchanger, often due to a failing pump or debris in the system causing the water to overheat too quickly.