I have a 12year old potterton suprima . It has been a good faithful boiler until 3 years ago when the radiators just stopped getting hot (warm it could manage ) and 2 radiators bairly that . System was flushed last year and pump is new . Can it be because there is no pump over run, boiler kicks on runs for about 2 mins then shuts off from wall thermostat ,water out and water returning red hot (boiler clonks and ticks) but radiators only warm ?
Am now fixated that the pump should run the hot water around the system for longer ie adding pipe stat or remote timer but started to read blogs that say pump over run simply dumps the heat and will not circulate it round the radiators once the boiler is off ?

Apologies if this is all a bit vague but trying just to post essentials if anyone is kind enough to respond can add any details required .