You might have a more modern Rayburn such as the Royale which has two
seperate burners one for the cooker and one for the boiler. In this case
it
is possible to control the units seperately.
As I said it is best to ask Rayburn for a true assessment and correct
answer!

John, you're right about contacing Rayburn and I'm going to call them on
Monday. But, as you point out, it is one of the more modern ones with a
separate boiler unit which is independently thermostatically controlled.

Whilst at the Rayburn site I noted that this type of Rayburn will support a
primary circuit working on pure convection up 20 metres in length. If this
is the case all I'd need to do is extend my existing primary circuit and I
don't have to bother with pumping it and all the attendant changes to
pipework, valves etc etc. Seems hard to believe which is why I want to
confirm with Rayburn directly.

Cheers

Darth