Andy,

Thanks for your response.

I have looked at the pointers you made and have established the
following:

The boiler fails to light immediately when I attempt to draw hot water.
Sometimes it can take minutes to light other times it just doesnt and
rather than waste water we give up.

The diverter valve works fine and there is no hot water escaping into
the CH system when hot water is drawn.

The green light flashes indicating there is a demand for hot water but
the boiler does not light up. The fan runs as if it is about to fire
up.

I noticed this morning that the water temperature, when I eventually
got some hot water through, fluctuated from hot to cold.

Many thanks,

Ben