In an earlier contribution to this discussion,
xena wrote:


Ok, a bit more information. I've found the cable that goes from the
thermostat downstairs to the heating system upstairs, and posted a
pic he http://www.ukosborne.co.uk/images/wiring.jpg
with the relevant bits labelled up.

What a nightmare! Do all the wires going into each white block join together
inside? If so, God knows what they have done - you have a very colourful
mixture!


I've found a PDF of the RTS1 here with a diagram that shows that it is
normally open.
http://makeashorterlink.com/?V2D8258C9

The switch is shown open on the diagram. That doesn't necessarily mean that
it's normally open - it's probably drawn in the "satisfied" position to make
it clearer where the switch is. You said there was nothing connected to 3
anyway.

You or somebody said that this stat contains a relay. I have a hunch or
theory - which may be rubbish - but may be worth checking out. Is the stat
*supposed* to turn on a zone valve which - in turn - turns on the boiler and
pump (as per S-Plan in the Honeywell document)? If so, and if there's a
relay coil between L & N in the stat, the relay coil may be (incorrectly!)
wired in series with the zone valve motor - which may *just* provide enough
current to motor the valve to the open position. When you remove the stat
from its baseplate, you would break this link, and the zone valve would
shut. Can you get someone to stand by the zone valve when you plug the stat
in to see whether it does anything? Which cable(s) in your junction box go
to the downstairs zone valve, and what are they connected to?
--
Cheers,
Set Square
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