Wiring UFH to existing y plan

[nohoper7]

Hi, Please bare with me. I have attached a diagram of the plumbing that has been done to create the UFH. and the current wiring diagram for the CH and HW,
My problem is i have heard alot about "bakfeed" to the mid position valve through the orange wire. Is there a wiring diagram including my new UFH out there somwhere that can help me wire it all.

Many Thanks

 

[HandySparks]

I'm nor a CH expert and this isn't a straight answer but, considering the situation when only the UFH is calling for heat:
Is the main circulating pump required to run when using the UFH? (I'm not familiar with the detail of UFH.) If so, should the flow to the UFH be teed off between the pump and the 3 port valve?
If the main pump is wired from the boiler (as it often is to allow the pump to overrun after the boiler is shut down) then it will run when the UFH is calling for heat. Will the 3 port valve shut off the flow to both the HW cylinder and rads or does at least one outlet stay open? If the valve never completely closes, you may choose to replace the 3 port valve with two 2 port valves. If you do this, it may simplify the wiring. The output switches on the Honeywell 2 port valves (which are the ones I'm familiar with) do not share a supply with the valve motors, so back feed doesn't arise.

Apologies for rambling on. Maybe you've considered all of this already.

 

[robsparky1975]

Am i right in thinking that the ufh is an extra zone,so if there is an existing 2 channel programmer,if there was a spare core in the wiring to the existing programmer,1 of these cores could be used for the ufh on,and at the existing wiring centre that would tie in with the roomstat for the ufh and the 2 port wired back there also,i did wire the same type recently and i remember they changed the existing y plan for 2 x 2 port valves,and another 2 port for the ufh,perhaps that has to be done,if you look on the sticky threads for ch there should be some diagrams that you can use,my thoughts are that it can affect the system with the extra zone so thats why they get changed to 2 port valves,a bit of pipework altering,if i remember right a y plan is hw priority.