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Pressure drop with condensing boiler (Read 2141 times)
thescruff
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Re: Pressure drop with condensing boiler
Reply #7 - Jan 31st, 2009, 3:39pm
 
12Ltrs/min is with a delta T of 35c, so if the mains supply is very cold which it has been due to the Arctic conditions, you can expect that to be lower, if you  want really hot water.

Most combi's will only supply one outlet at a time.
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CWatters
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Re: Pressure drop with condensing boiler
Reply #6 - Jan 31st, 2009, 8:09am
 
That boiler is specified to produce 12L/min if the mains is upto it. Try measuring the flow rate you get out of the hot taps. Turn on two taps at the same time and measure the flow rate on each while the other is still running. Add together. See if you get anywhere near 12L/min.
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thescruff
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Re: Pressure drop with condensing boiler
Reply #5 - Jan 27th, 2009, 11:11pm
 
edwardgeorge wrote on Dec 29th, 2008, 10:38am:
New condensing boiler fitted 1 year ago. Water pressure is ok [legal/authority requirement]. When shower is used & downstairs taps hot or cold used pressure/flow drops at shower & temperature sometimes changes. How can we overcome this please? A pump on th incomer?



Sounds like a typical Combi to me  :-X
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edwardgeorge
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Re: Pressure drop with condensing boiler
Reply #4 - Jan 27th, 2009, 8:13pm
 
Thank you everyone for your answers. It looks like I have to live with what I've got. The installer did check the mains pressure & flow & found it to be just on the minimum requirement for the Gloworm 30cxi condensing boiler. The boiler feeds heating & hot water for a 3 bed semi. Water board not interested in increasing incomer mains size without me taking out another mortgage.
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Re: Pressure drop with condensing boiler
Reply #3 - Dec 29th, 2008, 8:31pm
 
You can not put a pump directly on the water main.

From your post, I am assuming it is a combi and sounds like water main issue.  Installer should have checked pressure / flow rates.

Problem with accumulators is positioning them, they are the size of a water cylinder.

If your shower is not a thermostatic one suitable for use with a combi then change to one.
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CWatters
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Re: Pressure drop with condensing boiler
Reply #2 - Dec 29th, 2008, 2:44pm
 
I'm not a plumber but..

If running a cold tap drops the flow rate on the hot then that sounds like a problem with the incoming main or the pipework between main and boiler. Check all valves are fully open.

It sounds like you already suspect the incoming main is the problem... Have you measured the static pressure and flow rate where it enters the house?

1) If the static pressure is good but the flow rate is poor then two solutions exist. In order of preference.. a) New fatter pipe from main to house. or b) a pressure accumulator..
http://www.plumbingpark.co.uk/plumbing_hvac_article12316.html
http://www.modbs.co.uk/news/fullstory.php/aid/5100/Are_you_feeling_the_pressure_...

Note that I'm not talking about a thermal store. Sometimes those are also call accumulators.

2) If the main in the street is the problem and both the static pressure  and flow rate are low then it might be possible to use an accumulator with a pump but I've not investigated those.

The problem will be finding someone locally who knows how to test the mains properly and correctly specify/size an accumulator. I didn't need one but the plumbers who built my house had never even heard of them. They are similar to the expansion vessel on a central heating system only bigger.

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Re: Pressure drop with condensing boiler
Reply #1 - Dec 29th, 2008, 11:30am
 
The temperature issue can be improved by fitting a thermostatic shower, which should regulate the water temp when the water pressure changes.
As for pumping the mains, I am no expert but it is probably not advised. Your boiler can also only heat up a limited amount of water at a time so you may get luke warm water instead of hot.
I am sure one of the plumbers will be along shortly....
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Pressure drop with condensing boiler
Dec 29th, 2008, 10:38am
 
New condensing boiler fitted 1 year ago. Water pressure is ok [legal/authority requirement]. When shower is used & downstairs taps hot or cold used pressure/flow drops at shower & temperature sometimes changes. How can we overcome this please? A pump on th incomer?
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« Last Edit: Dec 29th, 2008, 10:40am by edwardgeorge »  
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