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/home...21%20V4073.pdf

Toby.

rest or mid position anyway, I see the normal S-plan wiring will do

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.