In an earlier contribution to this discussion,
Pete wrote:

Right - new problem (but I think I know the solution)

Just got the 2 port valve, and when having a look at the wire noticed
that the white didnt have an inner core (just a the plastic covering).

After checking the lid of the valve the diagram shows there is a
microswitch which just connects grey and orange when the valve is
open, thus we can fire the boiler when the HW is ON.

Am I right in thinking that this valve cannot be used without the NC
link to the pump heating?

After opening up the valve, I note that the "dummy" white cable is cut
short. I then consider swapping the relay for a SPDT, and after
looking find that one is already fitted but not wired? (why???)

I cannot connect the white wire as it is a dummy! so will need to
replace the 1m or so of flex to make a connection to the white.









For this you will need a 2-port zone valve and a tank stat on the
hot water cylinder (if you don't already have one). An I right in
thinking that to wire I need to:

Connect thermostat HW On to: Valve Brown
Permanent Live to: Valve Grey
thermostat CH On: Valve White and Pump L

Boiler L to Valve Orange

plus neutral & earth


Thus, boiler gets power when valve activated (via grey)
Boiler gets power when valve off (via valve white)

Currently the boiler has a connection for the pump. I assume that
this should be left so that the pump can continue to run when the
tank theremostat is cycling.

The wire colours may vary, but if you study the Honeywell wiring
diagram referenced earlier, and wire it *functionally* the same way,
you should ok.

If you're converting to a C-plan, the switch on the zone valve - which
operates when the valve opens - *needs* to be a changeover switch with NO,
NC and COM - otherwise it won't work. If your valve isn't like this, swap it
for one which *is*.

If, on the other hand, you're aiming at a fully-pumped S-plan system, with
*two* zone valves, the switches on those only need to be of the simple
on/off type.

--
Cheers,
Set Square
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