Your boiler's temperature sensor for hot water has stopped working correctly, meaning your taps and showers may not get warm or could stay cold.

Hot water thermistor open circuit

What causes this fault?

This fault occurs when the internal sensor responsible for monitoring your tap water temperature fails or sends an incorrect signal to the boiler's control board. The most common reason is that the sensor has physically degraded over time or developed a lime-scale coating, preventing it from reading the water temperature accurately. In some cases, the error is caused by loose or corroded electrical connections between the sensor and the main wiring.