Central heating programmer wiring

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I've got a static caravan with a Morco GB24ErP combi boiler, which has a built in tappet style timer for CH. I wish to add a Drayton Wiser system so as to have better control and more importantly be able remotely turn heating on when we are getting close to our holiday home.

The boiler has a link wire between 2 terminals labelled 'Room Stat / Timer', which in the manual are further described as '230VAC Feed' & '230VAC Return'. The manual states that if connecting a thermostat the link wire has to be removed and the thermostat connected across these terminals. I'm therefore assuming that my Drayton controller will only need to make and break continuity between these 2 terminals and NOT supply
230v (obviously after the link wire has been removed).

I'm happy to connect a 3A fused supply to the Drayton controller back plate, but would like confirmation of how to connect to the controller to the 2 terminals on the boiler.
My belief is that I need to connect terminal 1 (Com) on the controller back plate to the '230VAC Feed' terminal of the 'Room Stat / Timer' connections, then connect from terminal 3 on the controller back plate to the '230VAC Return' terminal of the 'Room Stat / Timer' connections on the boiler.
In the Drayton instructions there is an option to put a link wire from the L terminal to terminal 1 (Com) if power needs to be provided, but as all I seem to require is to make and break continuity between the boiler terminals, I assume that I shouldn't need this power supply link wire.

Hopefully someone with more experience in this field can either advise where my plan is wrong or reassure me that my plan should work.
 
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Looks like you have already sussed this out. As you say, all the thermostat receiver needs to do in this case is act as a switch and won’t need an additional Live link because the boiler is already providing this on one of the control wires.
 
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Thanks jackthom, am I right that terminals 1 & 3 on the programmer back plate are the right ones to connect to the boiler terminals?
 
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The simplist way to do it, is use the 4 wires connected to the boilers mechanical timer, L&N to L&N on the drayton and the other two connect to 1&3 on the Drayton either way round it doesnt matter, leave the thermostat link in place
 
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