My current timer for my gas heating is one of the clickety click pust out the tabs versions. I want to replace it with an electric timer, and was looking at the horstmann timers. I ahve 3 zones going from my boiler, upstairs rads, downstairs rads, and hot water, so i'm going to get the 3 channel timer H37Xl. the 3 zones are currently controlled by manual valves, so will need to change those, but no problems there. My question is about the timer itself. it controls 3 channels, for my 3 zones. but when a zone is switched on does it also switch on the boiler, or does the boiler need it's own channel? i guess the boiler is switched on whenever a zone is switced on, but just wanted to make sure