Yes there is. There is a temperature switch, which is supposed to stop the cycle when the water reaches the high temperature, as selected by the High switch on the boiler. If this is faulty then the boiler keeps going until the water is much too hot, hence causes all the banging and flow into the expansion tank. There is a second (safety) over temperature switch which eventually stops the cycle. I changed this High thermostat on mine many years ago and that fixed the problem. That was after CORGI heating engineer changed the water / heating motorised valve at great expense and to no effect. Note that there is a similar Low thermostat inside the boiler, which is selected by the Low setting on your boiler. It is unlikely that both will be faulty so you can leave it on low. My experience is that it is fine for the summer warmer months, but in winter it is insufficient. You will also find that it will take a lot longer to heat up a full tank of water when set on low. I have found I have to set my tank thermostat down from about 65 to about 60, to give it a fighting chance of reaching its goal.
Mike, August 2009
