Heating/DHW programmer wiring

[Frank]

I've changed an ancient Centaur Plus 27 programmer for a Drayton Wiser and I *think* I might have got the lives on the programmer (labelled 3 and 4) swapped over as the DHW is not turning on.

If I haven't got them swapped, and I check by swapping them now, will anything nasty happen?

[John Rumm]

Depending on how the controls are wired, and what type of valves you have, you may need to use the "HW Off" output rather than (or as well as) the "HW On" one.

See the circuit diagrams here:

Yup, a cold bath :-)

(but you are unlikely to blow anything up)

[Frank]

Thanks, the diagram was really useful. I was able to short the DHW stat at the wiring panel and the motorised valve didn't move. Looks like it's deceased.