To have TVRs on all rads one method is have an auto by-pass valve fitted
between the flow and return. Have a boiler which can maintain a constant
flow temp. Have a it set to 80C. Balance the system to 10C across the
rads
and boiler, if an existing system. Install a pipe stat on the boiler
return, so that the burner is off at 71C.

How is interlock achieved? You don't have a flow switch in this design.
Explain how the burner never fires if the outside temp is, say, 30C.

As it stands, this system will cycle, as when the water drops below 71C, it
will fire up again even if there is no call for heat.

Christian.