Hi, I have an oldish Valiant combination boiler (approx 15yrs old), which was serviced 2months ago! It got a clean bill of health, but recently the hot water only works when the heating is turned on. If the heating is not on the water temperature is barely luke warm, even if the heating is on the water never gets really really hot like it used to. Can anyone please help me? I would appreciate any advice you have...please bear in mind that I am a combi boiler novice so please use simple terminology.