Your boiler has detected that its temperature sensors are incorrectly placed or wired, preventing it from calculating how much heat is being delivered to your home.

Central heating return thermistor fault

What causes this fault?

This fault occurs when the boiler's control board detects that the temperature readings from the internal pipework are coming back in the wrong order. The most common reason is that the flow and return sensors have been physically clipped onto the wrong pipes or the wiring connectors have been swapped during a previous repair. Because the boiler cannot accurately monitor how heat is moving through the system, it shuts down as a safety precaution.