Your boiler is heating your radiators normally, but it is failing to provide hot water when you turn on your taps.

What causes this fault?

This fault happens because the internal mechanism that switches the boiler’s heat from your radiators to your hot water taps has become stuck or failed. Either the electronic motor has stopped moving or the internal valve has become clogged with debris, meaning the boiler doesn't 'realise' or physically cannot react when you turn on a hot tap. While your heating continues to work, the boiler remains locked in heating mode and cannot divert that warmth to your water supply.