Can anyone help? I had a strange fault on my combi, which is 10 years old and has been quite reliable, only having to fit an external expansion chamber last year. When the boiler is switched on the CH runs all the time despite the clock timer being in the off position and the control knob being on the "summer" setting of hot water only. I have fitted a new DV ans the plunger does actuate the micro switch when we use hot water. So I now have to turn the boiler off in order to stop the CH and turn it back on again if we need hot water or CH,, any ideas?????