"jon" wrote in message
...

Is this good or bad practice. Should I install isolation valves on the ch
flow and return and the dhw in/out, about 6 inches under the boiler
connections (obviously making allowances for the filling loop and it's
connectors, etc).

Haven't really thought through the benefits of this, or the cons
(un-nessecary restrisctions right at the start of the runs, maybe), but
just
thought I'd check with the group.

I'm guessing that there's no real need?

Isolation valves should already be on the boiler. If you are inserting a
strainer on the boiler return, the fit a "full bore" isolation valve either
side so you don't need to drain down to clear the strainer. After
commissioning clear the strainer one a week for two weeks , then once a
month for a few months. By then the loose debris from the old system should
have been picked up by the strainer. This crap which would have entered the
boilers heat exchanger. Also have a strainer on the cold water main supply
to the combi. Debris from the mains can enter too.