Spat wrote:
David Hansen wrote:
On 3 Oct 2006 05:27:48 -0700 someone who may be "Spat"
wrote this:-

more gravity fed shower fitting questions! [snip]

Also, I'm planning to branch off existing bathroom pipework, the
instructions for a mira realm says cold must come from a cistern, I'm
not sure if the cold is from mains or not, is that likely,
It depends on which part of which country the house is in and the
age of the plumbing. Perhaps 50/50 over the whole of the UK.

or even something to worry about?
It is very much something to worry about. Imagine the situation
where someone is showering under a non-thermostatic shower when the
mains water fails for some reason, but the gravity fed hot water
continues for some time. They are likely to be scalded, perhaps
killed.

It's certainly at higher pressure than the hot water.
Then it is highly likely to be from the mains. Follow the
instructions, someone went to the trouble of writing them for a
number of reasons including your safety.

If the shower is thermostatic and you wish to trust your safety to a
mechanical gadget, rather than doing the plumbing properly, then a
pressure equalising valve can be fitted to make the thermostatic
valve work somewhat better.


Thanks. I guess the water is at mains pressure then, my question was
prompted because nearly everywhere I've read, instructions for fitting
a thermostatic mixer shower from GFed suggested tapping off from
existing bathroom piepwork was ok, just the Mira instructions stating
different. Looks like I'll have to run a huge line from my loft water
tank, a right pain!

I've run showers off mains cold and tanked hot. They work,. Its illegal
though because any blockage can cause the cold water to backfill the hot
water tank and cistern. I think a non-return valve would fix that. Of
course its vile, because anyone opening taps anywhere alters the
balance, and the shower temp is all over the place. Even thermo showers
have a hard time coping.

In fact you can get curious effects like this on full pressure systems too.

As I discovered when I installed a mixer on ours, before fitting the
shower head. I left the head blanked off, but forgot to switch the
shower off after leak testing..it became a matter of pure luck as to
whether any given hot or cold tap would deliver hot, or cold water..in
fact most did both, at different times..