In message , Roger Mills
writes
Well yes, if it's still going strong after 30-odd years, I'm not quite
sure what you're worried about.

If it were my system I would try to contrive that, under normal
circumstances, the HW and CH are not being heated at the same time. You
then wouldn't have to worry about HW vs CH balancing and could remove
any restriction on the HW side, resulting in faster recovery. You could
achieve that by using the existing programmer to time the HW, and
inserting a programmable room stat to time the CH. [You really, really
*should* have a room stat]. Then, you could heat a tank of water each
morning before the CH comes on and, with a decently insulated tank, it
should stay hot for a long time.

Judging by the age of your boiler, and the fact that it's got two lots
of connections, it was probably designed with gravity HW and pumped CH
in mind. In that case, the boiler capacity will be such it's own stat
can stop it overheating without requiring pump over-run or a minimum
flow rate. You should certainly be able to do away with a pipe which
by-passes the HW coil.

I'm going to hit just these problems shortly and would welcome
advice/wiki info.

I opted for a thermal store rather than stress about Megaflow
maintenance issues. (My insurers want annual inspections for pressure
vessels, air compressors etc. so I can see where the interest lies.)

With underfloor heating and pretty much 24 hour occupation, I think
priority could be given to hot water. The manifolds come with a local
circulating pump but I assume a further circulating pump will be
required. The combi we have for our annexe here must have an internal
pump as the plumbers did not use the one supplied with the floor heating
kit.

Pumping over is a concern as the make-up tank is below ceiling height
(chalet bungalow).

I haven't yet met a plumber keen to take on the job!

--
Tim Lamb