Bang goes the CH controller

We need a few more details about your system - gravity hot water and pumped CH, or fully pumped? If fully pumped, how many - and what type - of motorised valve do you have? [Likely either one 3-port valve (Y-Plan) or two

Going from the last bit first - I have a single three port valve and a single pump (Y plan I reckon).

Replace the valve head and the time-switch/programmer. Check for water leakage around the 3 port valve and/or the wiring to/on the wall thermostat (if fitted).

I've taken the controller apart and put some photos online

There's an installation diagram up there too. It's the only installation method listed by horstmann to contain a three port valve so hopefully it's OK. Oddly though I have no room thermostat so presumably this controller wires from pin 4 straight into the valve - is this the culprit, or am I jumping ahead of myself?

Thanks,

Jon

Sounds like the valve and cable would be first on the list of things to check. Cables can get nibbled by unwanted guests. Less likely would be the room stat and then only if it is the type that has a neutral feed as well as live in and out.

Time to get the multimeter out!

If it looks like it is just the programmer that has decided on an early retirement (with extreme prejudice), then you can wire it out, and rely on the tank and room stats for control until you get a new one.

It's *possible* that there was a fault inside the controller itself - causing it to self-destruct when you switched the heating on - but it seems more likely that there was a short in the valve actuator. Unless you can rig up a means of testing the actuator on its own, the only safe solution is to replace both it and the controller. If you replace *just* the controller, and there *is* a fault in the actuator, you stand to write off the new controller.

Problem Solved! I changed the actuator from the mid position valve and the controller. I checked the actuator out with my multimeter but couldn't identify any differences to connections to wires coming in and out (by that I mean I tested the resistance between all wires and all were high) but I did think that the mechanism was rickety enough to have a connection between the electrical side of the manual open lever and the earthed metal case. Worryingly it was all dead when I first turned it on - the fuse in the plug that was powering the whole shebang had blown along with the mains tripswitch.

Thanks to everyone that contributed - this was the first "disaster" in the new house. Should any of you need any molecular biology help then drop me a line.

Jon