Hi, I am very inexperienced with central heating but have been having problems that get worse. NOW i have a boiler that works, but does not seem to heat the water or the radiators. The boiler lights up starts heating but then makes "kettling" sounds and turns off. I thought radiator pipes were blocked, put in sludge remover, left for several days then drained off each radiator and the drain above the boiler. Muck came out then clean water on each when it had run clean for a while I stopped. I was also told it could be the pump, I checked but it seems to be running vibrates when system on, the by pass valve may not be working, not sure on that. The pipes from the boiler up to the hot water tank get hot, as does the pump and pipes near it but still "a non working system". I was then told to isolate the pump and check if the ??inverter was working, no idea what this is, had a go at isolating pump, could not stop water coming out - now not confident that isolating valves are working/were turned the right way. Any helpful suggestions welcome - I can criticise and ridicule myself - lots!! HELP.....