UH8-RF wiring for UFH and Rads

4 Feb 2008
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United Kingdom
I purchased a UH8-RF with 3 Neoair stats to control a combi system with rads upstairs and 2 UFH zones downstairs in an S Plan format with 2 x 2 port valves.
Just looking at the wiring diagram on the UH8-RF and wonder why it shows using the boiler output along with the valve switch (grey and orange) on the rad 2 port valve but not using the valve switch (grey and orange) on the UFH 2 port valve?
I checked the output on the Boiler terminals on the wiring centre and it goes live on both radiator and ufh call for heat, Heatmiser confirmed this is the design in case the system has actuators rather than valves.
Would I not be better off just using the 2 valve switch (grey and orange) wires to call the boiler?
Otherwise the boiler will fire before the valves have opened. The system has a pressure valve to pass water if the valves aren't open but it seems to make more sense to me to not have the boiler just circulating water.
The only downside I could see is if the valve fails and the switch gets stuck, then the boiler will be continuously on.
Any help appreciated.
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