In article . com,
"JavaEnquirer" writes:
I've recently had a number of quotes for the installation of a new
condensing combi boiler and new radiators. Currently, we have an old
gravity fed system with 20 year old rads.

Some of the plumbers we've spoken to strongly suggest chemical or power
flushing the system and fitting a filter on the return to the combi.
However, the plumber we are feeling inclined to go with suggests just
letting the boiler run and water flushing. He said that he hadn't heard
of people fitting filters on the return.

Is it necessary to have a filter on the return if the system has been
water flushed and the radiators are new?

I would suggest it in the case of a combi, otherwise the
plate exchanger will act as a filter and unlike hard water
scale on the other side of it, the rust debris doesn't clean
out easily. If the whole system is new, or it's not a combi
boiler (i.e. no plate exchanger to block), then it's probably
not worth it.

--
Andrew Gabriel