I have a Vaillant Turbomax 824 combi boiler. Recently, when I open the hot water tap without CH on, the water goes hot and cold and hot and cold and so on. The CH supply pipe does not get hot when HWD is on without CH, I have tested that. I do not think it is the usual diverter valve problem. Any ideas?

Combiproblem, October 2007

Could be that the secondary heat exchanger is blocked on the central heating water side. Remove it and flush it through using a tap, but you may need a new one. Beware, its not always strightforward to get the right one

Matthew, October 2007

sounds like return ntc sensor is giving false reading or htg pipe to pump ( the one insidethe boiler behind combustion panel) is blocked

paul, October 2007

sounds like return ntc sensor is giving false reading or htg pipe to pump ( the one insidethe boiler behind combustion panel) is blocked

paul, October 2007