hot water cylinder - odd Shower connection ?

Definitely not. Apart from anything else, the actual heating circuit should contain inhibitor. Although if a BG installation, probably not.

In message , tony smith writes

Are you sure it is the mains? nt the CW cistern in the loft - running a shower with mains CW and tank fed HW isn't very good because of the imbalanced pressures (assuming standard copper HW cylinder)

Are you sure it is from the cylinder coil feed/return? Might it be an extra feed for the shower added to the tank - I have one (an Essex flange) fitted to the side of my tank , near the top, before it curves in.

I think a photo or two will be helpful here.

Post to webspace/Flickr/tinypic etc. and post a link

Are you sure its from the coil? A friend has just had a new cylinder fitted and it has a blanked off outlet about 7/8ths of the way up the tank labelled "dedicated shower off take - blank off if not required". It is in the side of the tank rather than the top, but it is close to the top. I have just googled to find an illustration but failed.

Although the design is different, Digram B on this page

might explain the presence of an off take close to (but not at) the top (ie to exclude any air from the shower supply)

Is the Surrey Flange more upmarket than an Essex Flange? :-)

I suppose it depends on what that "coil" really is... if its the indirect coil used for heating the cylinder, then no it sounds wrong. If however it were a large coil designed to allow the cylinder to be used as a heat bank - where heat is extracted from the stored water into cold water fed through the coil, then it might make some sense.

Some photos would help.

but the latter is much less likely

NT

I don't know how likely it is - but it does actually make quite a lot of sense!

If the cylinder *is* a heat-bank with a coil to heat the DHW (rather than the coil carrying primary water from the boiler), the DHW will be at mains pressure - and will thus balance the mains pressure cold feed when blended in the shower's mixer valve.

As others have said, blending mains cold with gravity fed hot wouldn't work very well.

However the HOT valve ( with a closed value.. ready to be connected to the hot water for a shower) comes from a pipe which is part of the cylinder coil (heat exchanger)

Which suggests it's not a separate outlet on the tank.

works ok here

NT

putting it

Stratification. A heat bank should be relatively tall and narrow. The solar coils are right at the bottom, the coolest part. The bottom of ours can be as low as 30 C with the top at 80 C.

The vertical alignment of the various tappings is important on our store (not evenly spaced in reality):

Hot HW out (coil) - Boiler ret.

Wood burner ret.

Cold HW in (coil).

CH flow.

Boiler flow - CH ret.

Solar ret (coil).

Solar flow (coil) - Wood burner flow.