I'm assuming that's already in place at the wiring centre. As I'm connecting the HeatLink into the wiring at the programmer end, then it's not relevant. Whereas Stem's point about the 'HW Off' being connected to the 'Hot Water Satisfied' is valid.
Finally tackled it today (wanted to wait until the other half was away for a few days in case it didn't go to plan).
All done and dusted in less than an hour. Everything connected and working like a dream.
Just wish I could've run a couple of wires from the Heat link to the thermostat, but got 2 door frames and walls in the way. Or replaced the existing thermostat and changed the wires, but wasn't possible. So at the moment the thermostat in on a table in the lounge. (I don't fancy having conduit on the wall).