So I drained my Central heating system today just to remove 1 radiator in a room I'm decorating. When I refilled the system the central heating nor the hot water will work. I thought it was the motorised valve so I replaced that but to no avail, so the valve came with a new 3 way port so I changed that too, still no joy. No other changes have been made to the system for over a year and no problems at all. The pump runs when the system is powered up and continues to run when hot water is called for but the boiler seems to go in to stand by after a minute or so when powered up. I've even removed the valve again and set the port to the mid position by hand. Nothing send to work, in completely stumped. Any suggestion please. TIA.