I moved into my current house about a year ago, and I'm finally getting round to working out why my central heating won't come on without the hot water heating on. The system is pumped with a mid position three port valve controlling what is being heated, so as I understand it there is no technical reason why I couldn't just have the CH on. We barely use any hot water from the tank, so it seems a complete waste to be heating 100-odd litres of water every day.
I think I have got to the bottom of why the mid-position valve won't allow CH only now. There is a wire missing from the programmer to the junction box, shown on this diagram from "HW OFF" to terminal 7
Its wired with two twin-and-earth cables so I'm one wire short.
Now my first question is: Is there a technical reason why the system would be installed like this? I suspect it is simply a case of the system was upgraded at some point in the past and this wiring was never replaced, but I don't want to go to the effort of resolving this if it's still not going to work.
My second question is can I resolve this without running a new cable? To do this would mean a lot of work to do a proper job, and its probably not worth the hassle if this is the only option. It would be easier to convert the system to the "s plan" setup which doesn't require that extra wire.
As I understand it, the programmer logic is if HW is on, the "HW ON" wire is live, if its programmed to off, the "HW OFF" wire is live. They're never both on simutaneously. If this is the case could I use a relay with the "HW ON" wire and the permanent live supply to terminal 1 - so when "HW ON" is off, the relay is switched to power terminal 7. I hope that makes sense! I'll draw a diagram if its not.
I think I have got to the bottom of why the mid-position valve won't allow CH only now. There is a wire missing from the programmer to the junction box, shown on this diagram from "HW OFF" to terminal 7
Its wired with two twin-and-earth cables so I'm one wire short.
Now my first question is: Is there a technical reason why the system would be installed like this? I suspect it is simply a case of the system was upgraded at some point in the past and this wiring was never replaced, but I don't want to go to the effort of resolving this if it's still not going to work.
My second question is can I resolve this without running a new cable? To do this would mean a lot of work to do a proper job, and its probably not worth the hassle if this is the only option. It would be easier to convert the system to the "s plan" setup which doesn't require that extra wire.
As I understand it, the programmer logic is if HW is on, the "HW ON" wire is live, if its programmed to off, the "HW OFF" wire is live. They're never both on simutaneously. If this is the case could I use a relay with the "HW ON" wire and the permanent live supply to terminal 1 - so when "HW ON" is off, the relay is switched to power terminal 7. I hope that makes sense! I'll draw a diagram if its not.
