Wiring Problem At Heating Programmer

[NozSpark]

If it's a back boiler the 3 port valve will not be visable. It's all quite easy really as hot water and heating are not seperately controlled. I had to re- wire one of these and it took a while.

Why would that be???

I've just helped my mate replace a back boiler fired CH system with a combi......the old 3 port valve was in the airing cupboard,, however there was a 3c&e going to the old back boiler!