DIY Doctor UK DIY Forums

I have a worcester 350 boiler which has recently been serviced.My hot water is fine but my central heating rarely works,most of the time the radiators all stay cold at the bottom.Sometimes the heating works ok and other times it swiches off after a short time (20-30 mins).I have thoroughly bled the radiators although I could not get all the air out of the one next to the boiler,it still had air in after bleeding for an hour.Any ideas guys,cheers

could be sludge in the rads make sure both valves are open the return and obiously the flow try bleeding the pump aswell just loosen the nut in the middle ever so slightly and be careful the water is very hot

Classic sign of sludge in the system, and even if you get it flushed, you need to cure the source of the problem--- air ingress, causing production of brown algae;-- can be seen in header tanks in vented systems. If it is just accumulated iron oxide from years of radiators rusting, a power-flush will be a good investment of £600, Or do it yourself with a litre of sludge-dissolving chemicals, circulated for 4 weeks at operating temperature;--- you need to drain a radiator + the header tank, recouple the radiator pipes, then add the chemicals (a good brand, and not the concentrate), at the vented-system header tank. Then allow this tank to top-up again, and prime the radiator you drained, and power-up the system, and flush hot water thro' just one radiator at a time, for long enough to get the bottom hot, then valve it off and move on to another,etc, until all are OK. When your task is done, the system needs emptying, flushing, and refilling with water, laced with radiator anti-rust additive. Priming rhe system can be a pain;--- makes the £600 fee for a firm to do the work look attractive! They can cure any leaky valves or couplings they find using a couple of strips of PTFE tape on each, or renew radiator valves if needed. A powerflush uses special chemicals and a separate pump, and takes less than a day, but you pay dear for a firms overheads. I have heard that the equipment can be hired, if you know where to go.