CH Programmer

Following on from a previous thread... I too would like to change my knackered mechanical programmer (15 years old) for a shiny digital version
I really like the sound of reusing the backplate - saves hassle
I have a Smith Meters Ltd Switchmaster 400 - a search on Google suggests this is now made by Drayton???
Only trouble is I don't know which programmer to replace it with If possible I would like one from Screwfix as it's cheap and just across the road !!! but they only do Horstmann or danfoss
Also the old switch only does HW on or HW plus CH on I would also like just CH at different times Would I be able to achieve this with the existing wiring? (I can open it up if anyone needs to know what's there
-- Regards
Hays
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hays wrote:

There are only 4 or 5 wires connected to most programmers - so it's not a big deal to re-wire if the new one doesn't have the same backplate.
As to whether you can have CH without HW, most programmers support this - but your plumbing may not. If you have a fully pumped system with either a mid-position valve to control the HW/CH flow [Y-plan] or two zone valves doing the same job [S-plan], it is possible to achieve. Have a look at the S & Y plan details in http://content.honeywell.com/uk/homes/systems.htm when all should become clear. You may need some minor wiring changes. In particular, for Y-plan, you will need to connect the HW-OFF terminal in the programmer to the appropriate connections on the cylinder stat and mid-position valve.
If your system *isn't* fully pumped (e.g. gravity HW and pumped CH) you can still achieve what you want - but only by installing an additional zone valve and thermostat, and re-wiring in accordance with Plan-C.
--
HTH,
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hays wrote:

They are both ok.

Depends on the system more than the wiring.

More than likely.. Don't be afraid of using a different make. The install instructions are very comprehensive and refer to most old models.
Generally the wiring has:- mains in to the programmer. CH demand HW demand HW satisfied ( for a 3 way valve)
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As far as I know there is no current equivalent programmer which will fit on the Switchmaster backplate
--
geoff

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You might want to consider leaving the CH on 24 hours and controlling it from a programmable thermostat instead. Much better control imho.
Colin M
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