On 15/05/2018 21:08, Roger Mills wrote:
Following on from the earlier thread about "pumping under", I'm
seriously considering converting my friend's system to unvented - making
it much easier to get the air out, and hopefully solving the circulation
problems. [And hopefully not introducing too many leaks as the result of
the higher pressure!]

I thought where the boiler is specified to work in an unvented system,
it was allowable to have a single 22mm pipe (20mm internal) as a cold
feed from the expansion tank to the system?

It would guarantee no pump under, or over!

Wouldn't that be simpler and allow the simple addition of Fernox etc?