PeterK wrote:
Spoke to a company involved in the "supply chain" today. Respecting their
straightforward and honest answers no further details of identity.
Aside from telling me the taps were ok to 5bar the background to the
confusing instructions is an allegation there are "a lot" of legal actions
in progress between consumers and the "sheds" over water leaks from taps.
Some consumers have bought and fitted "bottom end of the market" taps with
no thought as to their water pressure and with no legal max pressure in the
UK there have been some substantial bursts/leaks. IIRC 15bar was quoted as
the water pressure of one complainant. So saying the cold feed should come
from the tank and the H & C pressures should balance absolves the supplier
of any "high pressure" leak whilst at the same time sneaking in the non
return valve requirement to ensure the legality of plumbing into the cold
main.

Thanks for the responses

No! Thank you for that posting! It fills in the picture and explains
a lot. I'm now not surprised that writs are flying. With the extra
info, I would now be extremely wary of feeding mains pressure HW into
it.

BTW I don't doubt that any of these units can cope with mains pressure
- it is the ability to mix at mains pressure I doubt.

To add to info in my previous posting, one of these packaged 'free'
shower/tap units was fitted in the (new) 2nd bathroom around 5 years
ago. It's been on the list to sort out since then, but as it is seldom
used as a shower & due to lack of info, the job has been left in
limbo. (Well, it was a free lunch..)

The cold tap is plumbed into mains CW and the hot into a gravity fed HW
(around 2m head over the taps). The way these units work is either as
independant H & C taps or with a flick of a lever send both water
streams up thru the shower tube. On mine balancing H & C tends to be
hit & miss, but normally because of the excess CW pressure it is far
easier to make the mix too cold than too hot. From your posting that's
lucky, because it would seem there is a sever risk of scalding if mains
pressure HW is supplied.

Basically you have 2 streams of water heading towards each other & what
the mix is, is a matter of luck. My guess is that it must be extremely
difficult to control 2 water streams in this way, and the greater the
pressure the more the difficulty; plus the risk that the cold coould
suddenly fail leading to scalding.

Hence it seems to me that this type of bathtap/shower - at least in
its raw state - can only be safely plumbed into gravity fed H & C
system.

Even with this basic fitting method there's more that need to be done.
It is correct as a poster has said that the air gap in the water tank
means that SFA the water company is concerned there is isolation (it
makes a tundish) between the mains supply and the shower, so a
non-return valve is not strictly necessary. However contaminated water
COULD be back siphoned into your own private HW system & back into the
header tank. Who knows what could start breeding there. You don't
want that, so IMHO non return valves are essential in both H & C lines.

A second aspect is the position of the shower head. For the same
reason that ought to be restrained so that the head cannot fall into
the bath water . That used to be in the regs, but IIRC the requirement
has (unwisely) been dropped in the unified (EU) regs.

What else can you do? A quick look in the Screwfix catalog doesn't
reveal a relevant substitute combined fitting, but there are a number
of separate shower controls you could fit. You could seal off the
shower part of your taps and fit one of these units just above the
taps. Screwfix cost: most likely in the GBP100 to 200 range. (The
key words appear to be 'temperature contriol by ceramic disc'.)
Sub-GBP100 (30 up) are listed, but do they control flow and mix
properly??)

That's how I'll probably set about fixing mine. Making sure I get
proper mix/flow control & I'll probably add a pump into the HW line.

Many thanks for the extra info.