Your boiler is struggling to accurately measure the temperature of your hot water, which usually means it cannot provide consistent heat when you turn on the taps.

Hot water thermistor open circuit.

What causes this fault?

This fault occurs when the sensor responsible for monitoring your hot water temperature fails or loses its electrical connection. It is usually caused by the internal components of the sensor wearing out over time or moisture causing corrosion on the wiring connectors. Without this data, the boiler cannot safely regulate heat, so it stops producing hot water to prevent overheating.