Or use a 230V no/nc relay next to the joint box to provide the HW on/off commands, feeding the coil from the existing HW "on" wire.
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Replacing Potterton E2002 with Drayton LP722
Leesparkykent
Nearly Esteemed
Some good ideas and options. You can go back armed now lol 
D
davesparks
chances are there wont be a permanent live in the joint box
Leesparkykent
Nearly Esteemed
Had this problem a few times with Y-plans. Pain in the backside when you've been given a wireless thermostat/receiver to install.
Good point, if the programmer is near the boiler there probably won't be a permanent live at the jb.
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