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Keefiedee Keefiedee is offline
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Default Wiring diagram for fully pumped Honeywell S plan

So what you have *isn't* an S-Plan system - because that would only have
*one* pump.

With two pumps, you don't actually need any motorised valves. You simply
control each pump with its (room or cylinder) stat - and you then need some
relay logic to fire up the boiler when either (or both) pump is running.
[You may then find that you still get gravity circulation in the HW circuit
when only the CH is supposed to be on - in which case a simple check valve,
which requires pump pressure to open it, needs to be inserted into the HW
circuit.]
--
Cheers,
Roger
______

- Show quoted text -


I thought the difference between S plan and Y plan was that S plan
used 2 port motorised valves, and Y plan used 3 port valves?

Keith