Howdy again, Seems it's all falling apart at once in my plumbing system! When the boiler is running the 3 position diverter valve has started "clicking". The clicking noise is the microswitch being hit then the valve moving off it and then moving back and making contact with the switch again. A sort of rocking motion that means the microswitch is being hit every second or so. It happens when only the hot water is on and when the hot water and central heating is on. When only the central heating is on there is no problem. Any ideas?! Thanks.