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Author Topic: Low Cold Pressure In The Shower  (Read 1713 times)

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Offline chopsuwe

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Low Cold Pressure In The Shower
« on: August 24, 2014, 04:33:25 PM »
The cold pressure in our shower is very low, not much more than a trickle. I tried removing the shower hose from the wall and with the mixer on cold it is easy to stop the water with one finger over the end of the pipe. The hot pressure is fine, about what I would expect for a low pressure system. Only the shower is affected, all other cold taps in the house have plenty of pressure. If another tap is turned full blast the hot pressure in the shower will slowly drop after a couple of minutes and take a long time to recover.

It's an equal low pressure system without a header tank. My understanding is the water goes through a valve (3 in 1 valve?), a pressure regulator and then is split to the cylinder inlet and cold for the shower. The mixer is a Methven (looks like a Celeste Jumbo).

We had a plumber in who said he checked the filter(s?) and they were ok but wasn't sure what the problem was and said it could cost $400 to fix.

Any ideas what is wrong and how to fix it?


Linkback: https://www.plumbers.co.nz/forum/q-and-a-water-pressure/50/low-cold-pressure-in-the-shower/1743/

Offline Plumber

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Re: Low Cold Pressure In The Shower
« Reply #1 on: August 28, 2014, 09:16:25 PM »
Hi Chopsuwe, if he quoted 400 did he also say what that would encompass? There could be a series of reasons as to why your shower pressure is dropping off. Has the pressure always been that way or is it recent?
Please note that the advice I am giving is only my opinion and not necessarily a fact.  Please refer to our terms and conditions.

Offline chopsuwe

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Re: Low Cold Pressure In The Shower
« Reply #2 on: August 29, 2014, 09:03:15 PM »
He didn't say and I suspect he was just plucking a number out of the air as he really didn't seem to know what was wrong hence me asking here. A new mixer and UFO thing come to about $250 form Mitre10 (assuming I'm looking at the right ones!) so I really don't know where he got his figure from.

The pressure has been low since we moved into the house 9 months ago. Some days it's worse than others but it is never as good as the hot pressure.

Offline AlCan

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Re: Low Cold Pressure In The Shower
« Reply #3 on: August 30, 2014, 11:19:19 PM »
Hi chopsuwe,

You describe a very interesting problem.

You say the Cold pressure is much lower than the Hot pressure, at your shower wall outlet.

Do you have a two level house - is the shower upstairs and the HWC etc downstairs?

I can only think of two possible explanations so far, but if you give us more info about the levels and distances, that might help.

Anyway, if the shower is upstairs but the Cylinder and Pressure Regulator valve are downstairs, my guess is the Pressure is set (has dropped) too low. The valve may be old, and the spring has got tired. The explanation - cold water is heavier than hot water, so is harder to push uphill. If both hot and cold feeds to the shower come from the same regulator valve, then the regulator pressure must be only just over what is required to get the cold water there. I would suggest the pressure needs to be increased a fraction, but what's the setup first?

Is the Hot Water cylinder Open Vented? Is there a vent pipe running from the top of the cylinder up through the roof? If not, best not play with it...

The only other explanation I can think of for this strange behaviour is that there is some weird plumbing between the cylinder and the shower, and that for some reason, the cold line has developed an "air lock" - or at least, a partial one. For that to happen, part of the cold water pipe to the shower needs to run back downhill on its way up. Then, air can get trapped in the downhill section, and cause this kind of pressure reduction without completely stopping the flow. Seems unlikely that it would last for months on end, but strange things do happen. But I'd suspect the pressure valve first.

But, just for fun: Do you know if any other cold taps are fed from the Pressure Regulator valve? If so, you could try this. Turn off the Cold water supply to the Pressure Regulator. Turn on the Shower, to Max Cold. Find the lowest (in height from the ground) Low Pressure cold water tap in your house. Turn that full on and let all the water run out.  (If the water doesn't stop, it's not a Low Pressure tap...)  If it's low pressure, once the water has run out, close that tap, then turn the Cold supply to the Pressure Reg on again. Let the cold water to the shower run for a couple of minutes. You may get some air bubbles etc coming out.

See if that helps. If not, I'd say the Pressure is too low...

I note that you said that the plumber you asked only said "could" cost $400. Because he doesn't yet know what's wrong, and maybe he's thinking a new pressure valve, plus time to fit etc... Just to give you an idea of what you might be in for. Sounds okay to me.

Offline chopsuwe

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Re: Low Cold Pressure In The Shower
« Reply #4 on: September 01, 2014, 04:34:50 AM »
Thanks for the help, it sure is a curly one!

It's an open vent through the roof. The house is single story with the cylinder right next to the shower. I think the top of the cylinder is just a little higher that the shower head. The shower is the only low pressure cold, all the taps are mains. The regulator is below the cylinder and I think the pipe runs through the walls to the shower mixer.

If I lower the shower head to the floor the cold pressure improves a little. When it is raised back up to head height the pressure goes back down. If I do this with it set to warm the water temperature drops when the head is lowered (as expected as there is more cold pressure) and takes a good 30 seconds to recover when put back at head height

I should also mention that the cold pressure can improve or worsen slightly over a series of days.     

Offline integrated

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Re: Low Cold Pressure In The Shower
« Reply #5 on: September 01, 2014, 08:06:14 AM »
The first thing you need to determine chopsuwe is if the shower mixer definitely is or is not suitable for low pressure - its one thing for it to look like a methven celeste (which is suitable for all pressure) but is it really? there are plenty around that look similar and may make all pressure claims but are in fact mains only.

the quoted price is fair if it includes replacement of prv which may help

if the hwc is not on wetback then do away with open vent & re-plumb for valve vent setup

connections to mixer?

blockages?

air lock?

hwc cylinder could be plumbed better by looks?

trust your plumber - i know that may be hard for you to do - check his credentials, quals, licenses etc

good luck!

Offline chopsuwe

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Re: Low Cold Pressure In The Shower
« Reply #6 on: October 08, 2014, 02:04:45 PM »
The mixer is definitely a Methven, the model is harder to know because it's not written on it. All I've really got to go on is the shape of the handle and face plate. The house is well built so it's probably reasonably safe to assume they used the right sort of mixer.

I'm not distrustful of tradesmen in general but this the one that had a look at it really didn't inspire confidence.

If I was to replumb I'd rather put in an on demand system and reclaim the hot water cupboard space. My preferred option is just to fix the thing though!


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