No feed to the white wire.
It is fed momentarily when relay cuts in and then out.
By linking a 240v feed directly to the white wire it operates the valve, so from that I assume it's the room stat or the relay module or both!
I'm trying to diagnose a problem with my friend's CH.
It is a conventional gravity fed system, controlled with a Honeywell ST9400 programmer in conjunction with a HCW 80 room thermostat and HC60NG relay module.
The hot water side of things works normally.
I've performed the "teach in"...