Thanks for the explanation DP. My system seems to be working as you describe even without the white wire connected. The only thing it may be doing without me realising is that when it's heating the hot water and the CH kicks in it may not achieve the middle position. It may switch fully to CH...
I have just replaced the mid position valve in my gravity fed central heating system as it was partially seized. When I came to fit the valve control box which came with the new valve I noticed that the wiring for the old control box had the white wire not connected to anything. The wiring...
