2) The boiler is not designed to take luke warm let alone hot water as
it's input.

But I suspect most boilers would cope for the minute or two operation
period.

That is where the pipe stat and the timer comes in I suppose. Once the
loop is up to temperature it kills the pump and allows it to return to
heating mode. The big problem will be the heat capacity (or more the
lack of it) of the pipework - it will get cold quickly.

It only needs to be on for about one minute to heat the loop. Then the loop
will stay hot for many minutes with a high hysterysis thermostat satisfied.
Obviously any secondary circulation system would have to be very well
insulated. This applies to all types.

It will still cycle the boiler much more than a storage based system,
though. However, I don't see this as a show stopper, just a disadvantage.

6) The water bylaws
forbid the permanent connection of the mains to a closed circuit.

I can't see how this applies to secondary circulation loops. They aren't
really closed loops.

If a house needs a secondary loop it also needs a grown up heating system
that will include a stored HW of some type (vented, unvented or thermal
store).

Indeed ;-)

Whilst I'm no fan of permanently on secondary circulation loops in most
cases due to energy efficiency reasons, I can see the benefit of a manually
operated (i.e. 2 minute timed) system in a domestic property, as it would be
very effective at water conservation. A manually operated system would also
actually save energy, as the reheated water will start at a higher
temperature than fresh mains.

Christian.