So, one of the things I often have to install or in this case remedy is central heating wiring. In my experience central heating wiring is one of those things that has very often been installed by persons that actually do not seem to know quite what they are doing. Many the times' I've been called to fix an issue after someone else has been tinkering with it! Below is a reasonably simple two zone control or S plan system. However someone had joined both valves to a single thermostat. The terminal 2 seen below is actually a live return from a second wireless transmitter. I was called out as all the heating in the house was coming on in both zones regardless of the setting of the thermostat in one part of the house. I think this had been done as one of the valves was stuck open and so was in effect bypassed. I replaced the actuator on the 2 port valve and rejigged the wiring so it all worked as it should.

I've found that many electricians are unwilling to undertake work in central heating control centres as they find them a bit daunting. Personally I find them quite enjoyable to troubleshoot and get quite a few call outs to do so.