Thanks to all who answered my previous query about my central heating. It was the valve actuator that needed replacing. I am now thinking of replacing my CM 907 with a wireless CM 927. But this n eeds an additional live. The wiring diagram makes it look as though you can loop off the switched live. But I would have thought the switched live is only live when the stat is calling for heat. Is this a correct assumption, would it not be better to loop off the permanent live. Any thoughts would again be appreciated,
You need a permanent live to the control box. The switched live comes from the control box to the valve. You connect the permanent live to one side of the relay and get the switched from the other.
Where are you going to install it? It doesn't need to be in the same place as 907 'cos that's where you'll probably put the wireless bit.
If you can put the wired base unit near your wiring centre (airing cupboard?) you should have access to all the connections you need without having to do any 'looping'.
Ideally, it should be powered by a permanent live supply so that it maintains radio contact with the wireless unit all the time - not just when heating is required.
Then it needs a live feed, and it generates a switched live when there's an unsatisfied heating demand. You can re-route the wires which went to the 907 for this purpose. Incidentally, where did the 907 get its live feed from? Mine comes from a manual programmer whose heating channel is switched to 'Constant' so that the 907 does the actual timing. This means that I can turn the CH off (*really* OFF) if I want to without turning the HW off. [The 907's OFF isn't actually off under all circumstances because it still acts as a frost stat].
I'd agree with that one, having looked at the receiver power supply circuit for the CM927 it's not one I'd like to see cycled regularly, in fact I've had 2 units (in separate instals) lose their pairing (between stat and receiver) on power loss so I feel there's a bit of a surge susceptibility in the design.
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