does it matter if at the top of the hot water cylinder the 22mm pipe
that exists the cylinder goes in to a tee whose other 2 connections run
left and right (i.e. the pipe carrying the hot water to downstairs runs
horizontal until it bends down 90degrees and goes through the roof. the
other part of the tee again runs horizontal (well slight upwards
really, until it bends upwards and then over and cold header tank as
normal.

by theory is that since most diagrams and installations I've ever seen
have a tee, but is is positioned such that the vent pipe comes out of
the top of the tee, and the hot water exists the tee sideways, perhaps
there is a problem with my arrangement.

could the fact that both the hot water to downstairs and the initial
part of the vent part exist the tee horizontally mean that when the
bath hot tap is on full there is a sucking force applied to the water
in the vent pipe ?

I'm running out of ideas and this remains the one obvious difference to
standard installations that have the cold header in the loft and the
cylinder on the landing

wrote:
just as a test before replacing all with 28mm I connected up the cold
water feed from the cold header to the bottom of the cylinder also. (I
have two tank connectors on the cold header, 1 for hot and 1 for cold).
so essentially now both are feeding the bottom of the cylinder.

however, the vent pipe still easily sucks up water from a glass when
the bath hot tap is on full.

surely 2x22mm are better than 1x28mm so I'm stuck again since I'm not
convinved that 28mm pipe will make the situation any better.



Doctor Drivel wrote:
wrote in message
ups.com...
I've just moved my hot water cylinder to the loft. The cold header tank
is located above the top of the hot water cylinder tank, and the
connection from the lower part of the cold header tank to the cylinder
uses 22mm all the way, although has 3 90degree elbows.

I have a problem with air being sucked in the vent pipe to the ho****er
when the bath tap is fully open. I confirmed this by hold the end of
the vent pipe in a glass of water; all the water was eventually sucked
up when the hot bath tap was fully open

After reviewing several posts to this news group I read that the most
obvious problem is the poor flow from the cold header to the cylinder.
Most posts seem to suggest upgrading this pipework to 28mm, reducing
the number of elbows with bends, etc...

I have a couple of questions I hope someone can help with:

1: I didn't have this problem before when the cold header was in the
loft, and the hot cylinder was on the landing. am I right to think that
the flow from the cold header to the cylinder was under much higher
pressure because of the head of water. now both cold header and hot
cylinder are in the loft the head of water has been reduced
significantly from what is was before.

2: even if I upgrade the pipe to 28mm, I'm not aware of a fitting that
connects 28mm pipe to the 1inch cylinder connector. would I have to
convert the 28mm down to 22mm to connect it to the cylinder, and
therefore wouldn't this still be the bottleneck?

thanks for any advice or links to sites that sell the appropriate
connectors

Replace with 28mm and keep elbows to a minium. Bend if you can. 28mm
connectors are standard. http://www.bes.co.uk

You may want to fit a 28mm open vent too. This means more water in the pipe
to be dragged through the draw-off before reaching any air, then the cold
feed may have settled out. Also use full-bore isolation valves on the 28mm
pipe.