Separating zones on a single channel system boiler ...

5 May 2019
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United Kingdom
Just moved into and old house and trying to get the CH and HW bill under control.

The CH and HW run on two separately pumped zones but re-combine into one at the boiler for heating.

Current programmer has HW on as a constant default, with the option to have CH on in addition.

So the HW needs to be on to also then call for CH.

I am installing a Wiser smart therm with 2 zones.

The HW zone works fine as 'boiler live' and 'pump live' are connected (fires boiler and pumps HW to cylinder)

The CH zone doesn't (it cant fire boiler as not connected to 'boiler live' but does pump the CH circuit)

How can I insert some logic (relay?) to allow the smart thermostat to pass switched live to the boiler via EITHER the CH or HW live output from the smart control so I can run CH and HW separately.

Pic attached to help explain!


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Are you sure that you have two separate pumps? sounds like you have a gravity HW system or certainly that it was originally, it would be unusual to have two pumps an that system
You don't need two pumps, but you need two zone valves so you don't get "backfeed" when one of each zone goes live. This has always been achieved with the microswitch in the zone valve head.
This is a semi gravity system with an extra pump added.
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Two zone valve heads can also achieve the same goal (if you don't want to do plumbing in of the valve bodies)

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