# Fitting Thermo balance shower to combi boiler



## ByronBlack (30 Apr 2007)

Has anyone done this?

I'm looking to add a shower soon and just wanted to know if there is anything special needed to hook up the shower to the combi boiler. In the bathroom I have both the hot and cold feed pipes in the right location (there's a couple of plugged t-junction pieces from a previous install). 

I was hoping it would be as simple as adding some compression joints and flex-pipe from the hot and cold feeds and taking this directly to the thermo-balance shower, do I need any other kind of valves/hardware?

Any advice greatly received.


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## Dave S (30 Apr 2007)

Long time since I checked, but I _think_ the water regulations might require a double-check valve on any pipe fed direct from the main supply (ie not from a tank). IIRC the regulations are available online - when I get home from work I'll check if I have a URL.

Dave


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## ike (30 Apr 2007)

Hi Byron,

I fitted a thermostatic shower valve as you describe. The only difference being that I have a multipoint boiler (hot water only - no central heating). Due to very high mains pressure in my area I found the imbalance between the cold feed and the hot feed from the boiler made thermostatic regulation more difficult. I solved this problem by fitting a pressure-reducing valve in the cold feed to the bathroom (you could of course fit this specifically for the shower where you intend to tee-off. My local builders merchant supplied a valve with a suitably preset pressure, although they are easy to adjust yourself, for a little more you could even get one with a pressure gauge.

A gauge is not really necessary though since all I did was adjust the pressure setting so the cold-only flow was similar to the hot-only flow from the shower. Simply unscrew the blanking cap from the end of the valve body, screw the adjuster out until to reduce the pressure right down. With the cold tap on, screw the adjuster in gradually until the flow is similar to the max flow from the boiler.

PS. I _think_ it was screw _out_ to reduce pressure but was a while ago but it'll be obvious once you adjust it.

Never had any problem with it.

cheers,

ike


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## les chicken (30 Apr 2007)

You also need to check the spec of the combi to make sure that the hot water output is a constant temp and is suitable for a shower.

Not all boilers are suitable as the thermostatic shower valve is mechanical and will not tolerate changes in the temperature of the incoming hot water.

If that makes sense the way I have tried to describe it.

Les


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## ByronBlack (30 Apr 2007)

Some good tips there, thanks fella's.

Les, i'm a little confused. I thought that the thermostatic balanced showers account for differences in temperature from the hot and cold feed, so a constant temp is not nessacarily important from the combi - or am I barking up the wrong tree there?


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## ike (30 Apr 2007)

The boiler outputs at a set temperature (your setting) and regulates the burner to suit the flow demand (up to it's maximum capacity), so you don't need to worry what the boiler is doing - it does its bit automatically. The main bit is to avoid the hot/cold pressure imbalance as this will affect the ability of the thermostatic shower valve to maintain the desired output temperature. The PRV is the bit that allows you to 'tune' the thermovalve' response with the boiler pressure/flow characteristic.

It can take a little bit of twiddling with the PRV and the boiler temp setting to achieve a smooth, steady shower output temp, but rocket science it ain't.

Ike


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## les chicken (30 Apr 2007)

Ike I am not totally disagreeing with you but not all boilers are suitable for shower units.
The hot water output from some boilers are controlled over a range of temp, the better boilers have a themostatically controlled output. It is only this type of boiler that is suitable for a shower. The mechanical valve mixes the incoming hot and cold water to give the required temp for the shower. This water needs to be a constant temp as there is nothing in the valve to monitor the temp and to adjust if the water temp varies.

You also need to make sure that the shower is a thermo type and not just a mixing head.

Les


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## Sawdust (30 Apr 2007)

Byron,

It's never simple is it. We had a Mira 415 shower in a previous house and this was designed to work with a combi boiler where the hot and cold supplies would be at the same high (ie rising main) pressure. It worked well but if someone turned a tap on while you were showering you still got burned because the drop in pressure caused the shower to reduce the flow and when the flow reduced the water temperature increases. Things may have improved (this was about 10 years ago).

Make sure you get the right type of shower though, a normal mixer expects low pressure from a hot water tank and a cold supply from a tank as well. If you connect it to a combi boiler and the rising main, it probably won't work.

Also, i'm pretty sure the previous poster is right about the non-return valves.

Please keep in mind that I'm not a plumber so I might be talking complete rubbish but I have fitted a few showers and learned the hard way!

Good luck
Mike


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## Newbie_Neil (30 Apr 2007)

Hi Byron

Why not post your question here at the Ask The Trades site.

They're all good people, you just have to watch out for that Keith Smith. :lol: 

Cheers
Neil


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## woodshavings (30 Apr 2007)

Hi Byron,
I have installed exactly the combination you are asking about.
I fitted a thermostatic shower system, my boiler is a Bosch Combi.
It works fine. 

John


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## ByronBlack (30 Apr 2007)

Neil, thanks for the link, i'll go and check that out.

For purposes of this thread, here's the shower I was thinking about (after some initial research about the suitability):
http://www.screwfix.com/app/sfd/cat/pro ... 1&id=73743

Here's what the blurb says:

"Automatically compensates for variation in both the temperature and pressure of the inlet water supply to maintain the selected temperature to within ±1ºC."

So, does that negate the possibility of scolding when a tap is used? I got the impression that this was what it does and maintains a constant temp..


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## RogerS (2 Jul 2007)

Hi BB

Did you go for this in the end? Is it OK?

Cheers

Roger


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