I have an Ideal Classic FF230-280 Boiler on a ‘closed’ system. For some unknown reason the main circulating pump now never shuts off, even if the hot water and central heating are not called for on the timer. The only way to turn it off is to actually turn the main switch off on the wall. I have had a competent plumber look at it and he is stumped, I had an electrician out today and he checked all the wiring of the pump and 2-way valves and he confirms all is in order? Help!