That's an interesting possibility but I'm not sure if it would be
possible with our boiler. After living in a house with ducted warm air
heating for the last 35 years I'm seriously lacking in experience with
radiator systems so any comments and advice will be welcome.

One method that could be used is to separate the heating circuit from the
combi boiler primary, using a plate heat exchanger. Then, the new circuit
can have a full time alpha pump, flow switch or whatever, with all TRVs. The
flow switch, which detects flow through any radiator is used connected to
the combi as the call for heat. The system would work and be efficient, but
viability depends on obtaining a cheap plate heat exchanger.

+--------+ PHE
| -------------++-------+-FS----- to rads
| Boiler | || BP
| -------------++---------+--------
+--------+

= external pump, run continuously
BP = bypass (p. not required if pump is alpha)
FS = flow switch, demands heat from boiler
PHE = plate heat exchanger


Christian.