Hi

I'm about to fit a thermostatic shower and despite admitting to being a
relatively novice plumber, I am keen to learn and can generally pick
things up.

Although I have scanned existing messages, I cannot seem to find direct
advice on the following scenario...

I currently have a separate hot water feed from my HW tank to an old
shower that I am replacing. It T's off the main pipe from the top of
the HWT after a very short length. The main pipe is 22mm, the shower
hot feed is 15mm.

The cold feed to my bathroom is mixed. I have mains pressure, 15mm
cold to the toilets, sink and old shower, but the bath is fed from the
cold header tank in 22mm pipe.

The question I have is whether it is acceptable to connect the new twin
thermo valve shower to a mix of hot water from the tank and mains fed
cold or whether I definately need to add a separate cold feed from the
cold header tank (or T off the bath 22mm feed)?

Due to the existing pipe layout, it is going to be much easier to use
mains fed cold, but obviously, if that is not considered good practice,
then I'll have more work to do.

Thanks

Mike

"babs" wrote in message
oups.com...
Hi

I'm about to fit a thermostatic shower and despite admitting to being a
relatively novice plumber, I am keen to learn and can generally pick
things up.

Although I have scanned existing messages, I cannot seem to find direct
advice on the following scenario...

I currently have a separate hot water feed from my HW tank to an old
shower that I am replacing. It T's off the main pipe from the top of
the HWT after a very short length. The main pipe is 22mm, the shower
hot feed is 15mm.

The cold feed to my bathroom is mixed. I have mains pressure, 15mm
cold to the toilets, sink and old shower, but the bath is fed from the
cold header tank in 22mm pipe.

The question I have is whether it is acceptable to connect the new twin
thermo valve shower to a mix of hot water from the tank and mains fed
cold or whether I definately need to add a separate cold feed from the
cold header tank (or T off the bath 22mm feed)?

Due to the existing pipe layout, it is going to be much easier to use
mains fed cold, but obviously, if that is not considered good practice,
then I'll have more work to do.

Thanks

Mike

Most valves do require equal pressure on both feeds, although I have heard
of some specialised valves which do not. However, in this situation I would
consider a venturi shower; it uses the mains pressure cold to boost the flow
rate of the hot. A power-shower without a pump.

Bob

Mike wrote:


I'm about to fit a thermostatic shower and despite admitting to being a
relatively novice plumber, I am keen to learn and can generally pick
things up.


Having had repeat problems with an Aqualisa shower I "VERY VERY STRONGLY"
urge you to look at the manufacturer's install instructions for your chosen
shower.

I bought a house about 3 years ago which had had an extension including en
suite added just before sale.
The building work was OK but the plumbing apalling.

The tapping to the shower is taken from the top of the hot water tank
cylinder as you describe.
For showers that use any kind of accelerator pump (low voltage internal or
mains external), this is an absolute no-no!
The pump on our shower wears out in about 18 months!

So, I would advise: make an initial decision on the shower type you would
like, manufacturer, style etc., then look in detail at the requirements for
hot and cold feeds. If you cannot find specific install diagrams on the web
then ring the manufacturer.
You would not believe the amount of time I have wasted on our install trying
to locate the fault.
Swapping the shower to a different style after you have completed all
plumbing, tiling, enclosure building etc would be a nightmare.

Phil