Please can someone just advise me below?
While trying to work out what's going wrong with the 3way valve on our
central heating, I've been fiddling with the hot water cylinder thermostat a
lot, and it's become stiff. (no tittering...)
Is it a simple job to replace it, eg 2 or 3 wires, standard codes?
Current one looks like
and has a single white cable going into a 10-way honeywell connection box
in the airing cupboard.
The thermostat cable has 3 wires, red, black & grey.
Think of it as a simple changeover switch...one wire will be connected
to the "common" switch contact whilst the other two are connected to
the "normally open" and "normally closed" contacts.
Probably best to use a multimeter to work out which is which as there
are *possibly* different conventions in use with regards to colour
It doesn't really matter about the knob being stiff to turn - as long as the
stat turns on and off at the indicated temperature. You shouldn't want to
change the setting very often - haven't changed mine for years!
If you *really* want to change it, it's quite straightforward as long as you
get the right sort of stat, and wire it like for like. With a Y-Plan system,
it's *vital* that the stat is of the change-over type - and not just an
on/off switch. I don't know whether the Toolstation one is ok - it doesn't
give enough information.
The stat needs to have 3 connections - common, demand and satisfied. When
the tank temperature is below the stat setting, common is connected to
demand. When the tank gets up to temperature, the contacts change over and
common is then connected to satisfied. Without this connection, the CH won't
work after the HW gets hot.
When I said wire it like for like, I meant in terms of function. Forget wire
colours and contact labels - they may be different between the old and new
stat. Demand and Satisfied are sometimes labelled NO (normally open) and NC
(normally closed) or vice versa - so you'll need to work out which is which.
Thanks, that's good. I can use my multimeter to work that out, I was worried
about whether it had anything other than just a switch in it, sounds like
it's pretty standard to just be a c/over switch..
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