Adam - How does the Nest receiver fit to the boiler?
Claire - Same question, how did your Hive receiver fit to your combi?
Surely it depends on what boiler you have or is the receiver Universal?
My boiler already had a wireless thermostat so there was an existing receiver connected to the boiler.
I disassembled the old receiver and found that there were four wires that linked it to the boiler.
I reverse engineering it by looking at the old manual and figured out what each of them did.
I found that the new Nest receiver needed three them (live, neutral and call for heat), screwed them in the correct places on the Nest receiver and it worked.
You are correct though, when I looked online and watched a bunch of Youtube clips I did see that every boiler was different.
I don't know if he's still about but I ran a couple of things past L666KOP (think he's a central heating engineer or a sparky, can't remember) and he was very helpful.