Low Hot water pressure


Postby Debman » Thu Jan 22, 2009 6:11 pm

Hi,
I have a problem with low hot water pressure.
I have an indirect system, and the boiler is only 3 years old.
Cold water pressure is great. The cold tank is in the loft, and the hot cylinder in the airing cupboard underneath.
I understand from reading your "posts" that the pressure depends on the head of water going into the hot tank to force the hot water out.
I have brought a Grundfos domestic booster pump and fitted it to the cold feed to the base of the hot water tank in an attempt to increase the pressure in the tank, therefore, improve the hot water flow.
The pump is pressure switch opperated and runs when a tap is turned on. However, it has made no difference to the hot water pressure, and does not turn off when the tap is closed.
Would this work if fitted on the hot outlet side and draws out water, rather than pumping it in?
Am I just forcing water up the vent pipe, so not increasing pressure?
Also, since fitting this, my powered shower, which did work fine, is now stuttering badly.
many thanks
Debman
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Postby Stelf » Thu Jan 22, 2009 7:00 pm

Hi Debman
Not sure that the pump on the cold feed is a good idea. If the cold water tank is mounted on a platform placed on the joists in the loft and the cylinder is situated directly below on the floorboards in the airing cupboard then the pressure should be fairly reasonable. Have you checked your hot water outlet on the top of your cylinder for scaling and the cold water inlet to the cylinder for the same, which means, for the latter, draining down the cylinder first, of course. Also, is your cylinder mounted on a raised platform, which reduces the head of water?
Perhaps it is the gate valve on the cold feed to the cylinder which may not be fully opened. Any, or all, of these things could be the cause of the problem and worth checking first.
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Postby swidders » Fri Jan 23, 2009 12:44 am

The pump should be fitted to the top of the cylinder by using a surrey flange. As you correctly diagnose, you are only likely to be pumping cold water up i the overflow as it currently is. The pressure is determined solely by the head of water (level from water at top of cold-water tank and base of cylinder),with a 10m head giving you 1bar.

As stelf suggests, the problem may be a blockage of some kind, but i suspect it's just the head of water. The cold water may be working fine since (again guessing) these may be drawing their water from the mains supply and not the header tank.
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Postby Debman » Sat Jan 24, 2009 8:38 am

Thanks for the advice.
If I were to fit the pump on the outlet side of the boiler, do I fit it before or after the T that is the vent pipe?
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Postby nemo1966 » Fri Jan 30, 2009 9:28 am

[quote="Debman"]Hi,
I have a problem with low hot water pressure.
I have an indirect system, and the boiler is only 3 years old.
Cold water pressure is great. The cold tank is in the loft, and the hot cylinder in the airing cupboard underneath.
I understand from reading your "posts" that the pressure depends on the head of water going into the hot tank to force the hot water out.
I have brought a Grundfos domestic booster pump and fitted it to the cold feed to the base of the hot water tank in an attempt to increase the pressure in the tank, therefore, improve the hot water flow.
The pump is pressure switch opperated and runs when a tap is turned on. However, it has made no difference to the hot water pressure, and does not turn off when the tap is closed.
Would this work if fitted on the hot outlet side and draws out water, rather than pumping it in?
Am I just forcing water up the vent pipe, so not increasing pressure?
Also, since fitting this, my powered shower, which did work fine, is now stuttering badly.
many thanks[/quote]

Fitting a pump will not increase the pressure of your hot water to any real degree. It will increase the flow.
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Postby Debman » Wed Feb 25, 2009 6:51 pm

Hi,

both problems have now been resolved.
Fitting the booster pump to the :D outlet side of the hot tank has improved the water flow to the hot taps.

Running the feed from the top of the tank ( using existing pipework, not a surry flange ) has resolved the issue of the stuttering powered shower

many thanks
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Postby plumbbob » Wed Feb 25, 2009 7:09 pm

Fitting the pump on the input side of the cylinder will only result in the water being forced up the expansion in to the header tank without increasing pressure. This will cause all sorts of problems!!!

Fit the pump in the flow to the taps AFTER the expansion tee.
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