I have a Vokera 20/80 RS Flowmatic boiler which until today was working perfectly well. Now I'm suddenly getting no hot water from the taps. The boiler does not fire up when I turn the tap on like it used to. Pilot light is lit and the boiler fires up ok when I switch the CH on. I also get hot water when the heating is on so really the only problem is no hot water on its own. Is it likely to be a valve issue somewhere? TIA.