Leaving a Honeywell CH valve energised, wiring choices

Getting close to a combined UFH and rads installation fed from a condensing combi. I want to wire for UFH priority as that will have a greater operating window due to the setback temperature. Initial thoughts had been: use a second digistat to fire the boiler for the single UFH zone, pop a zone valve on the rads flow wired to the house digistat in order to fire boiler and open the rads when required.
Q1. Would it be better to use a mid-pos valve to achieve: Output to UFH / Output to rads / Output to UFH & rads -- it gives me a rads only option.
Assuming standard Honeywell colour scheme, looks like I will be leaving the grey 'hold in last position' live when no heat is required and I'm concerned that the orange output is listed as ~100v. Their guide does not recommend leaving the valve permanently energised, is it likely to be 'held' in the at rest or mid position anyway, I see the normal S-plan wiring will do much the same thing.
Q2. Is this good practice or am I reading too much into this? Q3. Providing the boiler switched live with 240/100v rather than 240/0v surely that can't be a good thing?
THis is the wiring logic: At rest > valve to port B (UFH) White live > valve to port A&B (UFH & rads) White & grey live > valve to port A (rads), 240v on orange Grey live > hold valve in last position, ~100v on orange
L Rads | On .__________________________ |_______./ ........... |White | Off ._ :Boiler : ......... | :Switched : :Mid pos: Port A >Rads | UFH :..L......: :Valve : Port B >UFH | On .____________|___________:.......: |_______./ Orange |Grey | Off .__________________________| L
http://content.honeywell.com/uk/homes/Catalogue/Heating%20Controls/2.21%20V4073.pdf
Toby.
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Meant Y-plan. (It was late, I was tired....)
Re-reading my question again. Honeywell and the FAQ don't seem to concur on the wiring, although I recognise that the definition of ports A & B are transposed between them.
Still a bit concerned about leaving the valve with 240v on grey(hold last position) for extended periods, and 100v output on orange is neither 'on' or 'off'.
Toby.
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