In an earlier contribution to this discussion,
Bodysnatcher wrote:

Hi.
I would like to replace our control unit that allows us to set the
time for heating/water to switch on.
The unit at the moment is a Honeywell.
Can not find the item number or a picture etc on any web site so
assuming they have discontinued it even though it's only about 12
months.
Basically it allows two periods of time each day but water and
heating are not independent, so when we have heating set, the water
also is on. This is the reason i would like to change it for a model
that has separate time settings for each, water and heating.
Does anyone know if wiring would be identical, as changing the wiring
is not my strong point but connecting up the wiring the same is not a
problem!


I assume that your existing programmer has separate controls for HW and CH -
enabling each to be switched to permanent ON, permanent OFF, or Timed - and
that the limitation is simply that they use the same timer - so you can't
have HW coming on at different times from CH?

Provided your plumbing setup is capable of supporting independent control of
HW and CH ** the way round this is to replace your mechanical room stat with
a programmable room stat - such as the Honeywell CM67. You can then leave
CH turned on permanently on your existing programmer, and *actually* control
the on/off times with the programmable stat. You can continue to use the
existing timer for HW - which can now be turned on and off completely
independently of the CH.

** If your system is fully pumped, and has zone valves (S-Plan) or a 3-port
mid-position valve (Y-Plan) you can do the above. If you have a gravity hot
water and pumped central heating system, it is a bit more difficult - but
not impossible - and requires additional plumbing hardware.
--
Cheers,
Set Square
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