I currently have a Rayburn cooker/boiler which heats the hot water cylinder
in
conjunction with an oil fired boiler if I desire (the hot water tank has two
primary coils one
for the rayburn and one for the oil fired boiler) This works nicely. The oil
fired boiler
does the central heating.

The rayburn circulation is done by gravity no pump involved. If I want to
allow
the rayburn to do some of the central heating (useful if the hot water
cylinder has
got fully hot) how could I integrate this into the central heating circuit.
Ideally I would like to continue to allow the rayburn to heat the water by
gravity and
have a pump cut in once the hot water is hot to circulate the heat into the
central heating
the separate radiator circuit.

My question is how should I arrange my piping/valves from the rayburn to do
this?