Whats the difference beteen an RB1 and an RB2 (in laymans terms)? Drayton got all technical on my ass!

Are these wired external of a boiler?

What are they designed to do? as my sparkie seems to think I'm gonne need one to run my UFH pump in parallel with the internal combi pump

What sort and how many wires/connections do they have?

Can anyone draw me a wiring diagram so I can get the idea?

Question, questions, questions...............

Hope you can help!