That is a pain. I agree you need another wire!
The system should have been done to the wiring regs, so I don't understand why you've ended up like this, unless due to 'organic growth' of the heating.
The 'borrowed neutral' is not the proper way as I'm sure you appreciate. In this instance it would work because both loads are on the same breaker, but not recommended - those more knowledgeable might like to comment?
Would it be practical to move the programmer to be nearer the wiring centre?
Alternatively if you were considering updating the system, eg to control individual radiators, then wireless could solve the issue.
The system should have been done to the wiring regs, so I don't understand why you've ended up like this, unless due to 'organic growth' of the heating.
The 'borrowed neutral' is not the proper way as I'm sure you appreciate. In this instance it would work because both loads are on the same breaker, but not recommended - those more knowledgeable might like to comment?
Would it be practical to move the programmer to be nearer the wiring centre?
Alternatively if you were considering updating the system, eg to control individual radiators, then wireless could solve the issue.