Thermostatic Shower advice

[babs]

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

[Tractorboy]

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

[TheScullster]

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