return feed

After some repairs done (twice) to prevent leaks from the bath pipes, the bath plug no longer closes properly. It was working perfectly before the 2nd leak was fixed. There was a little extra 'play' on the turn so with very slight pressure you could make sure the plug was sealed. I informed...

I've always just assumed that the colder the return to the boiler the more efficient the boiler would be (i.e. greater differential so heat transfer through manifold is faster). But I've come across direct evidence to the contrary (e.g. boiler recommends minimum 60 degree return, 'hearth' temp...