Your boiler has lost its connection to the hot water tank sensor, meaning it cannot tell how hot your water is and may stop providing it.

Short circuit in tank sensor | NTC defective, earth leak/short circuit in cable loom, damp plug connection

What causes this fault?

This fault occurs when the boiler can no longer communicate with the temperature sensor inside your hot water cylinder. The most common reason is that the sensor has developed an internal electrical failure or the wiring connecting it to the boiler has become loose, damaged, or damp. Because the boiler doesn't know how hot the water is, it stops heating the tank to prevent overheating.