Your boiler is providing central heating as normal, but it has stopped producing hot water when you turn on your taps.

No HW But CH Ok

What causes this fault?

This fault occurs when the internal mechanism responsible for switching the flow of heated water between your radiators and your taps has become stuck or failed. The most common reason is that the diverter valve has seized due to a buildup of debris and sludge within the system, preventing it from moving into the hot water position. This means the boiler continues to heat your home but cannot redirect that heat to your hot water taps.