"xena" wrote in message
...

"Set Square" wrote in message
...
In an earlier contribution to this discussion,
xena wrote:


Does that mean that the heating doesn't work either - or has the stat
been
by-passed in some way?

The heating does actually work. As long as the face plate of the
thermostat is on, the heating works. If it's taken off, then it doesn't.
I don't know why that's the case! The only thing I can think of is that
maybe one of the wires is a "satisfied" wire rather than "call to heat"
hence why it always thinks the heating should be on?

Um, how significant is the fact that the heating is on?? Does it mean that
I need a weird reversed thermostat?!

The type of stat which you have *needs* 4 wires, and can't safely be
installed with 3. A common short-cut employed by some plumbers is to use
the
green/yellow wire for the switched live (which you refer to as the "call
to
heat"). This is unsafe for two reasons. Firstly the stat needs to be
eathed,
but isn't when this is done. Secondly, a wire which any reasonable person
would expect to be earthed is, in fact, live!

TBH, the thermostat is plastic cased, and if I sleeve the wires with the
correct colours, would this be so bad? After all, the rest of the wiring is
likely to be to the same standard and I'm not replacing the lot as the house
is for sale!


If you want to do this properly, you have 3 choices:
1) replace the 3-core cable with 4-core
2) run a seperate 4th wire from the stat to whatever it connects to
(possibly a junction box in the airing cupboard)
3) replace the stat with one which needs less wires. For example, modern
electronic programmable stats only need *two* wires - since they don't
need
to be earthed and they don't have a built in accelerator heater needing a
neutral return.


Um, of all the above options, I prefer number 3! I think the RTS7 works
with 2 wires, so maybe I'll get that.

Is this still an option if, as it looks like, my wiring seems to be
"reversed" (i.e. it's constantly on even when the wires aren't connected, or
is this normal?

In order to find out exactly how yours is wired, you need to find the
other
end of the cable, and see what each of the cores is connected to. If you
can
identify the type of system you have in terms of one of the "plans" shown
in
http://content.honeywell.com/uk/homes/systems.htm you can look at your
stat
connections with reference to the appropriate wiring diagram.

I've looked upstairs, and our heating/plumbing system is a nightmare! We
have two circuits, one for the downstairs heating, and one for the upstairs.
There are wires everywhere, and nothing is labelled. The only thing I found
which might be of any use is "EARTH = N" written on the plasterboard behind
the connection to the upstairs thermostat.

Cheers
xena