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Techmonkey 09-20-2010 05:48 PM

Very odd loss of pressure house wide when tub runs.
For reference, here's our layout in our townhome:

1st floor - Shower, sink, utility sink
2nd floor - Kitchen sink
3rd floor - Tub, two sinks, shower (same room)

Our water pressure is fine house-wide running any tap or machine (dish washer, washer) except if we run the tub. About two weeks ago, the tub tap started acting strange with an abrupt change. Both the hot and cold tap are affected by this.

The symptom:

If we turn on the hot/cold/both for the tub, water pressure sustains a normal rush for about five seconds. After that the pressure rapidly tapers off to about 10% of what it normally would be. After the pressure drops, all other taps on the 2nd and 3rd floors are a strong dribble at best. Taps on the 1st floor are about 50% normal. If the shut the tub off, water pressure rapidly (a couple of seconds) builds back up on the other taps. If the turn the tub back on we get the quick rush of normal pressure that tapers off again just as rapidly and drops pressure throughout the rest of the house.

Trying to apply my electronics training to this (water and electricity are similar in theory, but don't mix well in reality.), and am stumped. :beer:


budro 09-20-2010 08:36 PM

sounds weird. i do know that tub spouts are the one outlet for water inside your house that has no aerator to save water. all sinks have them. your shower has them. they are the little round disks which have several preforated holes in them. they allow water out but under a restriction. energy saver. sounds like you are getting an initial flow of built up pressure which depletes when the tub spout is turned on. has anyone turned your water on and off at the meter lately? possibly didn't turn it all the way back open. has the water department worked a broken line in your area lately? a clog in the line could hurt your pressure. you may have had just enough pressure before to be ok and a small difference from somewhere seems to have a big effect now. could your plunger which turns your shower on be broken inside the spout or valve assembly? if it was fine before and now it is different means something is up. dig deep. thanks, budro

Techmonkey 09-21-2010 06:26 AM

Hey Budro,

Thanks for the reply. That's one of the possibilities I've been considering. I've been wondering if perhaps the water pressure coming into the house has decreased. I'll have to do some reading and see how I can test the incoming water pressure. Maybe that will give me something to go on.


Redwood 09-21-2010 07:06 AM

Hey Mark,

I'll give you a little explanation in electrical talk because you are right they are very similar.

Think DC...

Somewhere in your water supply you have a high resistance that is causing an voltage/amperage drop under peak load...

This resistance could be bad switch contacts or, a partially broken stranded wire.

Plumbing talk: partially closed valve, galvanized pipes choked with rust, debris clogging the pipe at some point.

The higher pressure when first turned on is stored voltage in a capacitor discharging keeping the voltage up...

Plumbing talk: probably a thermal expansion tank on a water heater or, the pressure tank if on a well system in which case a whole new can of worms gets opened.

Are you on municipal water or, a well system?

Techmonkey 09-21-2010 10:27 AM

Hey Redwood,

Thanks for the reply. I am on a municipal system. As for the clogging, it seems odd that it would be house-wide only when the tub is on. That part seems to me to be more of a short to ground. :D Since I don't have a heavy leak in the system, I'm starting to wonder if there has a mild drop in the water pressure coming into the house. Just enough where the closer outlets run well enough, but when you apply the biggest drain in pressure on the farthest point that it becomes evident. Not sure if plumbing can work that way though.

Redwood 09-21-2010 12:37 PM

Well yes it is more than likely a bad connection somewhere between the power source (city main) and the rest of your circuits (fixtures).

As soon as you close the switch to that 1/8 ohm 400 watt resistor (the tub) the circuit voltage (pressure) drops to 0 volts because the lack of supply....

So you see, you just have to find the problem, you are on track.

Any fixture or hose bibb not having a problem will be on the other side of the restriction.
If you have a PRV (pressure reducing valve) it would be a logical place to start.

Usually they are found between the meter and the other fixtures. Think of it as a voltage regulator.

Techmonkey 09-22-2010 06:36 PM

Found the oddly possible source of the issue! I realized I hadn't checked on my water softener in a few months. Looks as though I'd been out of salts for some time. I replenished the salts and ran recharge on the softener. Since then, the pressure has been back up. I'll test it a couple of more days to confirm. Thanks again for the replies!

Techmonkey 09-22-2010 06:37 PM

Well, I guess not all that odd since the WS is in series with the rest of the plumbing that feeds the house.

Techmonkey 09-23-2010 09:12 AM

Confirmed. Pressure dropped again and a recharge put pressure back up. Did some reading and it sounds like the filter material in the softener needs to be replaced. I'm not surprised since it's been about five years since last service and the filter material is 12 years old. Thanks again for the suggestions and help!

picolin 11-17-2011 10:30 AM

I have the same issue
I just wanted to drop in to say that I am having the same issue, but with the salt receptacle full. Water pressure would start OK, then drop after a few minutes (in the shower) or a few seconds (in the yard). Yes, I know, the yard shouldn't be softened, but I just moved this year and that's how they had it set up.

I'm going to check tonight if I can find where the filters are. I don't know much about Water Softeners, so hopefully it's easily accessible...

Anyway, thanks for pointing me in the right direction!

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