Hi, Rads are out of balance. the heated water is taking the path of least resistance (the ones that are very hot!) and returning to the boiler and the temp of same is switching the boiler off. Presume that this is not a new system so could well be that the pump is now not working properly. bleed pump by large screw in body, undoing just enough so that air, followed by water, comes out. If pump okay then rads need to be balanced. Before doing this, bleed them all. Commence balancing by fully opening the isolation end of all and then, with system running turn the lockshield end on the really hot ones first to induce resistance into the system. The warm ones should get hotter along with the cold ones. Just then a matter of "tweaking" until all at same temp.
Strevs
September 2007
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