On Wed, 19 Aug 2020 13:03:56 +0100 (BST), "Dave Liquorice"
wrote:

On Wed, 19 Aug 2020 09:26:38 +0100, Mike Halmarack wrote:

Can you post a photo showing what it looks like?

https://i.postimg.cc/LssWL0T3/rising-main.jpg

Look closely the upper (black pipe) compression joint still has a
turn or so to go before the flanges meet. Presumably these ones are
tight and don't fail. The lower (blue pipe) looks to be as tight as
it can go as the flanges are together, this probably means that the
pipe isn't fully held and these joints fail.

It might be possible to find the correct sized sealing/gripping
insert/olive for that fitting and pipe size. Simply replacing those
so the joint can be tightend before the flanges meet may well cure
the problem.

If the whole vertical run of this pipe is not mechanically
supported then the compression joints will be constantly
trying to pull themelves apart, which is not good.

This is three floors?
How do compression joints "pull themselves apart" exactly?

The last plumber who came around said that as the pipes flexed during
changes in pressure and on and off use, the joints worked loose.
This is made worse by bits of disimmilar pipe being connected
together.

Different sized pipes shouldn't be a problem provided the fitting is
correctly sized for the pipe.

Also that the pipework is just hanging there, instead of being held
firmly in place by various possible means.

Even providing support for the weight of the pipe work may reduce the
frequency of failure. The joints may not be perfect but until the
pull out or get close to pulling out don't leak?

Every little helps on the road to good enough.
--

Mike