I just want to check with the Brains that my thinking is correct.

The boiler has four connections for external expansions, and one of
these is a spare.

The three remaining connections are shown as Ns, Ls and Lr

The diagram of a mechanical stat with heater show the Ns as "neutral"
and going to one end of the heater.
The Ls is "live" and goes to the other end of the heater and contains
an open switch symbol in line.
The Lr line is "Switched Live" ang goes to another terminal in the
stat.

The usual link is across the Ls and Lr connections.

The receiver has three connections on it and these are marked
"Live", "Output" and "Neutral"

So looking at the two,

Ns = Neutral

Ls = Live

Lr = Output????

HELP???