Not surprised you're having trouble. It's a Priority Programmer you're replacing which is less common than the current 2 channel type. Need to know what motorised valve(s) you have in the system - probably honeywell V4044C - go have a look.
Right. But you should be able to wire it like W plan (see honeywell site) which is Water Priority (a slightly odd sort, in many people's minds).
I don't know if the 4044 valve body is the same as the 4073 which is the std 3 port valve (just being the head different) - or not.
W plan isn't popular. I'd be tempted to tell them the control system is obsolete and it now needs reconfiguring with a new programmer AND valve. As you can see from the wiring diag, you do already have all the wires you need in the connection box, for Y plan.
There are 7 in the connection strip. You might need pump live separated out too - what's the boiler?
You're going to have to label all the wires which go to the 3022, eg cylinder stat normally closed is on 3022 terminal 5's wire, and common is wire on terminal 2 , then put them on the appropriate terminals on the 715. etc etc
Cylinder stat common goes to HW ON terminal on the 715, etc