# Poor pressure!



## davies20 (Feb 22, 2009)

Hi all.

We have recently had a new bathroom fitted which we are more than happy with, this included a new 'drench' head shower. The problem is - is that this seems to have amplified our problem of having weak water pressure in the shower.

I've been told due to the shower running off the combi boiler pumps cannot be used?

Is our only cure upgrading our boiler?

Thanks in advance


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## fatdazza (Dec 29, 2010)

davies20 said:


> Hi all.
> 
> We have recently had a new bathroom fitted which we are more than happy with, this included a new 'drench' head shower. The problem is - is that this seems to have amplified our problem of having weak water pressure in the shower.
> 
> ...


Combi bolier heats the water as you use it. Unless you increase the rate at which your boiler can heat the water (changing your boiler, but even then there is a limit to what combi boilers can supply) you are stuck.


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## Sambcfc (Jun 8, 2015)

Is the shower run off a pump or is it straight off the combi? Depending on the size of the shower head, the bigger surface area the poorer the flow will be out.


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## Sambcfc (Jun 8, 2015)

What size boiler (kW) do you have?


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## Pip66 (Dec 17, 2014)

A Drench shower and a combi, will never work !!!!

You could try a higher KW input boiler. It may work, it may not !!!!

Also, is the in coming main up to the job ????


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## Clancy (Jul 21, 2013)

Boiler is the issue mate, can't supply what you need


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## m4rkymark (Aug 17, 2014)

Is the flow only weak in the shower? What's the flow like from your kitchen tap? Was it weak before you put the drench head in?


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## ffrs1444 (Jun 7, 2008)

Don't need a new boiler you just need a pump fitted pretty cheap via screwfix etc


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## fatdazza (Dec 29, 2010)

ffrs1444 said:


> Don't need a new boiler you just need a pump fitted pretty cheap via screwfix etc


You fit a pump on the outlet of a combi boiler and see what happens:lol:


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## davies20 (Feb 22, 2009)

Cheers for the replies. Not sure what KW the boiler is. Regards pressures, hot tap pressure is OK I guess, shower pressure has always been OK, just not as strong as we would like, but then this drench head shower, even using the flexi pipe head attachment is weak.


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## davies20 (Feb 22, 2009)

fatdazza said:


> You fit a pump on the outlet of a combi boiler and see what happens:lol:


This is what I was thinking lol


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## Rayaan (Jun 1, 2014)

davies20 said:


> This is what I was thinking lol


I've got an industrial pump fitted to 2 combi boilers. Pressure is INSANE lol


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## davies20 (Feb 22, 2009)

Rayaan said:


> I've got an industrial pump fitted to 2 combi boilers. Pressure is INSANE lol


I've always been told / under the impression an inline pump on a combined will do nothing?


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## dholdi (Oct 1, 2008)

If you want advice rather than conjecture then you need to measure your standing and dynamic pressures and flow rates. The duty of your boiler would also be useful.


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## rf860 (Jul 24, 2011)

Sounds like the kW rating of your boiler is only just capable of supplying a regular shower. These rain showers need good pressure coming to them to make them flow even reasonably well.

You're options would be either change the shower or upgrade the boiler. 

On a side note, it would be worth checking if the installer has opened the isolator valve going to the shower hot water pipework fully. This would be really easy fix if it wasn't fully opened!


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## Sean15 (Jan 13, 2016)

Did you remove the filters in the new shower unit, bin them right away. You will find them in the shower body itself where the connections go. 
Also is the shower the correct one, make sure its not a gravity fed one by mistake.


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## dholdi (Oct 1, 2008)

Hangs head in despair.


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## davies20 (Feb 22, 2009)

dholdi said:


> Hangs head in despair.


What's this all about??!! :lol:

Thanks for all the advice above, looks like I've got a few things to check when I get home from work 

Much appreciated.


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## macca666 (Mar 30, 2010)

Pip66 said:


> A Drench shower and a combi, will never work !!!!
> 
> You could try a higher KW input boiler. It may work, it may not !!!!
> 
> Also, is the in coming main up to the job ????


Have to disagree though I'm not a plumber or anything.

We have a drench shower in our house along with two 10.5kw electric showers.

The drench works off the combi and obviously the electrics don't but the pressure in the drench is better than the electrics.

My understanding is that the power/size/output of the boiler needs to be sufficient for the amount of radiators you have plus the shower. Also the distance the shower is from the boiler will affect it though as I said I'm not a professional and can only go on advice I got when we were installing.

My boiler is downstairs my drench shower is upstairs.


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## Rayaan (Jun 1, 2014)

davies20 said:


> I've always been told / under the impression an inline pump on a combined will do nothing?


No idea - not a plumber but this is how the plumber explained it.

Bit of background - 2 combi boilers in the cellar and live in a victorian house with 3 floors (4 including the cellar) so you can imagine it takes some effort to get the water up to the 3rd floor for the shower and even the sink!

Anyway, had a normal pump fitted 2 years ago by the same plumber, he said it should be OK but it was having issues with the shower and radiators on the top floor.

So he got an industrial one and it all works. In the bathroom the water comes out of the drench shower head so hard that it gives you a massage when its on full blast


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## davies20 (Feb 22, 2009)

right, the boiler is a Vaillant Ecotec Plus 831.

By the looks of things its a 25KW from what i can find online.

We have 8 Radiators & 1 bathroom with mentioned drech head.

Boiler is downstairs, bathroom upstairs.


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## 182_Blue (Oct 25, 2005)

davies20 said:


> right, the boiler is a Vaillant Ecotec Plus 831.
> 
> By the looks of things its a 25KW from what i can find online.
> 
> ...


Whats the hot water flow rate though ?


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## davies20 (Feb 22, 2009)

182_Blue said:


> Whats the hot water flow rate though ?


Rated or actual?

Not to sure how i measure the actual tbh


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## dholdi (Oct 1, 2008)

davies20 said:


> What's this all about??!! :lol:


I'd been on the red wine 

To measure actual flow rate get a container of a known volume and time how long it takes to fill it.
To measure pressure you need one of these:-
http://www.ebay.co.uk/itm/WATER-PRE...016620?hash=item43e680e86c:g:oZAAAOSwhglTx7K~
Fit to a bath tap and turn on gives you static pressure, leave that tap on and open another will give you dynamic pressure.
The boiler will do between 10.3 and 14.5 l/min of hot water dependent on temp rise.


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## davies20 (Feb 22, 2009)

dholdi said:


> I'd been on the red wine
> 
> To measure actual flow rate get a container of a known volume and time how long it takes to fill it.
> To measure pressure you need one of these:-
> ...


fair enough!!

right the Flow rate test seems easy enough.

Pressure test i might just have to get a plumber friend around for!

either way i want to get to the bottom of the problem!


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## davies20 (Feb 22, 2009)

looks like a unvented hot water system might be what we are after due to there being 5 of us in the house.

Anyone had any experience of these?


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## dholdi (Oct 1, 2008)

You would need a system boiler to run an unvented cylinder.
But yes they would give you large amounts of stored hot water.
If you had a cold storage tank as well you could run a pump for the shower.


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## davies20 (Feb 22, 2009)

dholdi said:


> You would need a system boiler to run an unvented cylinder.
> But yes they would give you large amounts of stored hot water.
> If you had a cold storage tank as well you could run a pump for the shower.


I thought it was the cylinder that did the heating of the water??


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## dholdi (Oct 1, 2008)

davies20 said:


> I thought it was the cylinder that did the heating of the water??


It does, with a coil that's connected to your boiler or immersions.
Unless you are talking about a gas fired water heater ?


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## Prydar (Jul 22, 2015)

Combi boilers work off mains pressure so if you fit a booster pump BEFORE the boiler it will act as if you have high mains pressure, that's all you need to do

Also after you fit a booster pump you may notice that the shower won't be as warm, this will be due to the water passing through the boiler quicker therefore giving the boiler less time to heat the water up, to counter that the mixer in your shower will be adjustable to let more hot water through rather than cold. To get to the Allen key that adjusts this setting you will probably have to take off one of the Allen keys that holds the mixer shower unit together

2nd edit but I thought this may help: Even if you fit an unvented cylinder this won't help your pressure problem because both unvented cylinders and combi boilers work off mains pressure, there will be no difference in flow rate between a combi and an unvented cylinder at all, the ONLY difference that fitting an unvented cylinder and system boiler would make is that you would have hot water ready for you which allows you to have a lower KW boiler, if your combi boiler is 28KW and above and can't imagine you having any problem with the heat of the water anyway

3RD EDIT: I'd just like to note that pressure and flow rate is a completely different thing, it's hard to describe but imagine if you had a 6 bar water main and a valve slightly open, the flow through the valve would be slow but it would eventually reach 6bar, and then as soon as you open a tap the pressure would drop massively and you'd then get low flow rate as the water wouldn't be able to pass the valve quickly. Flow rate is hindered by valves not being open properly, too many fittings in the pipework or small bore valves (a small bore valve mean that even if the valve fits onto a 15mm pipe the middle of the valve might only have a 10mm bore for the water to pass though)

I hope all that helped and that I won't need to edit this again!


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