Worcester 9.24 electronic Boiler H/water prob?

Hi

The central heating works fine but recently the burner would go off a few minutes after turning on the hot water and now switching on hot water taps does not ignite the boiler and obviously the water is cold.

I have been told that this may be the diverter valve, if so is this reasonably easy to fit and are they easy to get hold of?

Is there anything else it could be?

Many thanks for any help