Heatmiser UH8 volt free with a 230v switch wire boiler

[raidingKilt]

 

[davesparks]

Why is there a nest and a room stat I The diagram?
and why have you linked the room stat to the HW on from the nest?

Use the permanent live to feed the volt free switch to be sure of not getting a back feed there.

 

[raidingKilt]

Why is there a nest and a room stat I The diagram?
and why have you linked the room stat to the HW on from the nest?

Use the permanent live to feed the volt free switch to be sure of not getting a back feed there.

The nest is the heating system clock/programmer I have just popped the names in rather than drawing.
The ‘room stat’ is just a label as per a s-plan wiring diagram.

Circuit 4 (room stat on a s-plan diagram) is the ‘heat enabled’ output of the UH8, effectively the “room stat”.
There’s is only ONE hot water storage and ONE pump. So at some point the CH circuit and the HW circuit must merge so the one system pump and boiler can fire.
There are no 2-port valves or relays.

I have found the issue and all working correctly.