In an earlier contribution to this discussion,
altheman alan@ford50(no spam).freeserve.co.uk wrote:

hello, this may a stupid question to some but to me it is not...i have
recently moved into another house...the current central heating
system is run with a ...RANDALL 4033 PROGRAMMER....it has 2
switches...one that controls the hot water...the other controls the
central heating ( radiators)...what i can gather the PROGRAMMER is
approx 20yrs old...but still seems to work perfectly...my question
therefore is....do i need to put both switches down to run just the
central heating ?..for just the hot water i only put 1 switch
down...but someone said that to run the radiators i had to put both
switches down...even if i only wanted radiators on and NOT hot
water,we also have a BAXI gas fire with a back boiler ( if that is of
any importance)..many thanks in advance

In the unlikely event that you have a fully pumped system - in which case
you will have one or two motorised valves and a tank stat - you will have
independent control over HW and CH and will be able to have either without
the other - or both together.

In the more likely event that you've got gravity HW and pumped CH, they are
*not* independent. You can have just HW (by running the boiler without the
pump) but you can't have just CH - because you need the pump *and* boiler
for this, and get HW thrown in whether you want it or not.

You can probably still select just CH on the programmer, and it will work -
because most programmers used on this sort of system have an internal link
which switches HW - i.e. the boiler - on even though *you* haven't switched
it on.

As others have suggested, why not suck it and see?
--
Cheers,
Set Square
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