In an earlier contribution to this discussion,
AK wrote:

Related to the "Jobs are too small" thread below. I have been
encourged by some of you to at least have a go with trying to do the
thermostat myself with your help and guidance, so here goes!

I currently have a Drayton room stat like this one
http://tinyurl.com/25kle

I want to replace it with Honeywell CM67.

I have looked at the wiring on the Drayton and it is as follows:

Blue wire to N
Red wire to L
Earth (green & yellow) to earth
Yellow wire to a terminal numbered 3

I have looked at the instructions (and I've looked inside) of the
honeywell, there are 3 terminals, which is my first confusion as I
have 4 wires! They are labeled (A), (B) and (C). On the
instructions there are 4 wiring diagrams that are double dutch to
me!! I have looked at the honeywell website to see if they have
installattion manuals I can refer you to but they don't for this
thermostat, just the RF version which looks very different from this
one.

I know this is a popular thermostat as I got the recoomendation from
here, so hopefully some of you will be very familiar with it and you
can tell me exactly which wire goes where and what I do with the left
over one????

Thanks in advance.

Angela

You only need to connect 2 of the 4 wires to the CM67 - the other 2 are
redundant.

Firstly, the CM 67 does not need - and has no provision for - an earth wire.
Secondly, it doesn't need a neutral connection - and the neutral wire must
*not* be connected - otherwise you'll get a dead short under certain
conditions. [Your old stat has an accelerator heater inside to improve its
response, and the neutral provides the return for that. Digital stats don't
need internal heaters]

The built-in switch is a change-over switch which has a Common connection
(A) and two further contacts (B and C). When the room temperature is below
the set temperature, A is connected to B. When the set temperature is
reached, the contacts change over so that A connects to C.

However, for straight heating, you only need to use it as an on/off switch -
and only need to use terminals A and B. So, connect the red wire to A and
the yellow wire to B - and chop the other 2 wires off.

When I fitted mine, I put it in a slightly different place from the
original, and had to extend the wires. So I terminated the original cable in
a 4-way junction box inside a cupboard, and then used a 2-core cable for the
extension to the stat. Works a treat!

Come back if you start having fun programming it!
--
Cheers,
Set Square
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