glow worm 65-80 central heating works but no hot water?

Dear All, our glow worm 65-80 is playing up. the central heating appears to work as before and all the radiators get warm. The hot water does not get nearly as warm as it did. This is a sudden fault and not one that has developed over a period of time. I am aware that the boiler has not been serviced for a while. Can this be done by a competent person?