Wiring in a CM927 wireless stat

26 Apr 2006
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United Kingdom
Would appreciate any advice/guidance on wiring in a CM927 into my current installation.

This consists of a Halstead Finest Gold combi-boiler with room heating controlled by a Drayton Digistat 1. Everything works fine but the stat is badly sited so "going wireless" could help in this regard.

The Drayton has a single cable to it with red, blue, yellow and earth wires. The blue is connected to the Drayton's terminal 1, the red to its terminal 3 and the yellow and earth wires are taped and not used.

Looking at wiring diagrams it seem to me that the CM927 needs the above but with the addition of mains supply from a convenient point.

All advice/guidance gratefully received.

Many thanks
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Do you have the built-in mechanical clock on your boiler? If so, the override switch needs to be set to I, continuous, as the CM927 will take provide all the timing facilities.

Yes, the CM927 receiver requires its own mains supply to the L and N terminals.

A and B terminals on the CM927 receiver should be connected to the same terminals on the boiler as the Digistat (order is not important). See page 18. diagram 28 of the Finest/Gold Installation Manual It's the two terminals on the right.

Do not put any link between L and A on the CM927 receiver.

Check communication between the programmer and receiver before fixing in place. The easiest way to do this is to connect the L and N terminals of the receiver to a long lead with a 3 pin plug the other end. Plug in to the mains and move the receiver to various suitable locations until you get reliable communication between the programmer and receiver (see CM927 Installation manual for instructions).

If the receiver is near the boiler you can get the mains supply from the boiler mains terminals. In which case use a 4 core + earth cable, so that two cores will be the mains supply to L and N, and the other two will be the control cables to A and B. Earth is not used and should be made safe at both ends.
D-Hailsham. Thanks very much for an excellent, informative and helpful reply. Now clear what I need to do

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