Your boiler has detected an issue with the sensor that manages your hot water, meaning you will likely only have heating or very inconsistent water temperatures.

DHW sensor failure during No DHW function (CH OK)

What causes this fault?

This fault occurs when the internal sensor responsible for measuring the temperature of your hot water fails or sends an incorrect signal to the main control board. The most common reason is that the sensor has physically degraded over time or developed a wiring fault, preventing the boiler from knowing how hot the water actually is. As a safety precaution, the boiler will often stop providing hot water to prevent accidental scalding.