Home Pressure Test, where does the water go if not a leak?

[Vich500]

I'm going crazy & need some professional advice from someone who doesn't stand to profit.

After turning off water, our PSI drops from 65 to 61 in 2 1/2 hours. So; about 1.2 PSI per hour.

I've turned off every toilet angle stop, the refrigerator, washing machine feed, and used TP to ensure no hose bibb, bath, or faucet is dropping. I've removed the toilet hoses to ensure those angle stops aren't leaking. I've even installed a shut-off valve on the 20' of pipe feeding the kitchen slab - all other pipes are in the walls & upstairs flooring.

When I test to see how much water constitutes a 4PSI drop, it's about 2 tsp. So if it's leaking, it's a tiny seep.

I tried the same test turning off the ball-stop valve to the hot water heater, to eliminate pipe expansion issues.

I'm in So Cal. It's a perfect 70 degree day, so I doubt it's thermal freezing or over heating issues - outside is basically the same temp as inside. The feed for the house (only exposed pipe) is on the shady side of the house.

The question is, should I call a plumber for such a small drop or is there some other explanation? Would a plumber be able to locate such a tiny leak, if there is one? If there's even a small leak inside a wall, it could add up to mold & wood rot so it's worth fixing, but it could be a wild goose chase spending hundreds with nothing to show for it.

Wife's about to shoot me for delaying our flooring project, but now would be the time to be lifting subflooring if that's needed. Help!

 

[James Henry]

If theirs any air trapped in a pipe or fixture when you turn the water off the air may have compressed and reduced the water pressure. The real test is to leave the water off for an extended period and if the pressure continues to go down then you have a leak ,but if the pressure drop stops at a certain point then you don't have a leak.

 

[Sponsor]

 

[LLigetfa]

When I test to see how much water constitutes a 4PSI drop, it's about 2 tsp.

Expansion/contraction can account for more than that.

 

[Vich500]

If theirs any air trapped in a pipe or fixture when you turn the water off the air may have compressed and reduced the water pressure. The real test is to leave the water off for an extended period and if the pressure continues to go down then you have a leak ,but if the pressure drop stops at a certain point then you don't have a leak.

Nice insight. Thanks! Hadn't thought of that.

I mentioned that I'd left it off for 2 1/2 hours, so by "extended period", I assume you mean for something closer to 8 hours. Based on that rate of drop, it should drop by about 15 PSI if there's a leak. I'll give it a try.

 

[viper1]

I agree with above to leave things off for a longer period. However, I will make the assumption this is a municipal supply and you are shutting off at the meter? One thing you need to do is check the pinwheel on the meter. If it turns at all, there is water moving. You can also record a meter value and check back in several hours to confirm. I can tell you a few yrs back we confirmed and repaired a leaking main service line in the ground where the leak was bad enough to kill a tree, yet no visible water. It was concluded that water followed a close by gas line trench bedded in sand. I believe the suspect tree's root system played a part in the issue as it is pretty rare with HDPE pipe.

We confirmed the issue by cutting the main in the home and installed a plug to double confirm the valve was not leaking by. After that test, the yard was dug up and it was replaced.

If you have an actual leak in the home, I would think you would be seeing some evidence somewhere.

 

[Vich500]

I agree with above to leave things off for a longer period. However, I will make the assumption this is a municipal supply and you are shutting off at the meter? One thing you need to do is check the pinwheel on the meter. If it turns at all, there is water moving. You can also record a meter value and check back in several hours to confirm. I can tell you a few yrs back we confirmed and repaired a leaking main service line in the ground where the leak was bad enough to kill a tree, yet no visible water. It was concluded that water followed a close by gas line trench bedded in sand. I believe the suspect tree's root system played a part in the issue as it is pretty rare with HDPE pipe.

We confirmed the issue by cutting the main in the home and installed a plug to double confirm the valve was not leaking by. After that test, the yard was dug up and it was replaced.

If you have an actual leak in the home, I would think you would be seeing some evidence somewhere.

Thanks for the heads up. I'm not testing the main. I'm trying to determine if there's a leaky pipe in the walls or upstairs flooring before we install new flooring.

We have a Phyn Whole House Leak Detector installed just after the main. I turn off the water electronically using my Phyn app.

I'm also not testing the toilets as I've turned their angle stops off during my test. I'm also *not* testing the 25' of under-slab copper as I've also shut that valve off during my test. If we have a slab leak, my plan is to use the epoxy treatment to repair it.

Side note on Phyn. It does a nightly 6 minute pressure check. I've noticed that if I run hot just before the test, pressure can RISE tremendously. On one test, it went from 66 to 110 PSI! The Phyn aborted the test when it detected the unsafe condition. I have to wonder if that hasn't happened on some of the automated overnight tests since we delay our 3 hour dishwasher runs to overnight. Seems like Phyn should lower that threshold - 110PSI seems dangerously high, even momentarily. Especially if repeated often.

 

[Reach4]

Side note on Phyn. It does a nightly 6 minute pressure check. I've noticed that if I run hot just before the test, pressure can RISE tremendously. On one test, it went from 66 to 110 PSI! The Phyn aborted the test when it detected the unsafe condition. I have to wonder if that hasn't happened on some of the automated overnight tests since we delay our 3 hour dishwasher runs to overnight. Seems like Phyn should lower that threshold - 110PSI seems dangerously high, even momentarily.

110 is not dangerous at all. 130 is not dangerous. Turn on a faucet, and the pressure is going to drop quickly. This rise in pressure is due to thermal expansion as the WH heats the cold water brought in as you used hot water.

Note that the size of your thermal expansion tank affects how high the pressure gets. So does the size of the WH, and how hot you heat your water.

Set the expansion tank air precharge to the water pressure the city supplies. Precharge is measured and set when the water pressure is zero.

For your pressure drop tests, maybe you should turn off the WH and let the water cool down before doing your test.

 

[viper1]

LOL, I will not agree with above at all. Those pressures mean something is wrong. I don't care that the piping is "rated" for it, you have to look at everything connected to that. You are asking for it.

You are also trying to use some sort of "device" for a basic leak test. A good plumber could prove this out in 30min with simple testing. I told you to look at the service meter but you want to rely on something else. This is not rocket science but it is not as simple as "x psi loss = x volume of water loss"... The math does not work that way.

Absolutely not should your water pressure be climbing like that. Expansion tanks were designed for exactly that purpose and for good reason.

 

[LLigetfa]

Absolutely not should your water pressure be climbing like that. Expansion tanks were designed for exactly that purpose and for good reason.

My guess is the OP either doesn't have an expansion tank or the tank is waterlogged.

 

[Fitter30]

2 tsp water loss 4lbs of pressure loss. Like others wrote everything has to be at the same temp and longer time. Even draining the house down and using compressed air pressure will vary with change of temperature.

 

[Canada_DIY_Plumber]

Found this old thread. Curious how it ended up... Did you do the extended test?