Your boiler is struggling to heat your hot water tank because it cannot detect or communicate with a required external sensor or control module.

Without auxiliary function for DHW loading

What causes this fault?

This fault occurs when the boiler's control system loses its connection to the sensor responsible for monitoring your hot water cylinder. The most common cause is a faulty temperature probe or a break in the wiring that prevents the boiler from knowing how hot your water is. Without this information, the boiler stops heating the water as a safety precaution to prevent overheating.