I have wired in the nest and connected up the permanent live and neutral. What I am struggling with is the 'call for heat' wire. I am unable to work out where I need to wire it into. I have tried on the feed side where the red wire is looped round (room stat / timer) but it doesn't seem to be working and just stays on. Could someone advise me on this please - How do i disconnect the current thermostat and make sure the nest is now controlling the call for heat. Many thanks in advance.