Glad you got it sorted, but can you explain the fourth wire at the cylinder stat when there's only three terminals. I've got a couple of theories, but am I right I wonder?
H
hav it
cylinder stat is like two way switch. One live feed in from programmer HW ON, but two switched live outputs (not at the same time) One direct to boiler and one to grey wire on valve. thats 3 wires so the 4th may well be a earth. 4= earth
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