Low Pressure After Deep Freeze in New Construction with No Sign of Leaking

[Leo_S]

I did most of the construction on a new Detached Accessory Dwelling Unit that passed final inspection about 8 weeks ago. I hired a professional plumber to do my ground work under the slab on grade, and I did all of the plumbing above ground. The new DADU's water line uses an existing 3/4" copper line fed from the main house's basement that formerly ran out to a number of stand pipes that were removed. After the ground works and the slab was poured, the excavator operator crunched my copper line in the middle of the yard when digging a storm drain pit. So sad. He patched it with plastic pipe. I ran clear Uponor PEX throughout the DADU using expansion fittings. I ran the 3/4" main line up to a loft space where I have a "smart" shut off, pressure reducer, water filter, another shut off, HWH, and a recirculating pump for HW. My plumbing inspectors said I did a great job. That's the back story.

A couple weeks ago, we had record breaking cold weather here in Seattle with temps dipping into the teens with highs in the mid 20s for nearly a week. The ground froze solid. And the water was barely coming out of the faucet. I use the DADU as a work space and go there during work hours. After a moment of panic, I started trying to think where the pipes had frozen and what I could do. The supply line from the house is about two feet deep. But, of course, I had done some excavation for a window well on the house and hadn't finished backfilling, so the pipe was covered by about 18" of dirt on top and only 8-12" of dirt along the side for about a five foot stretch. And then, I realized that my pipes that go up to the attic come within a couple inches of soffit vents and could easily have frozen there too. I let the faucets drip for about 5 days waiting for the thaw to come. The pressure slowly came back, and I was feeling like maybe everything would be fine. But, for the last 4-5 days of 40-50 deg weather, the pressure has plateaued. I'll turn the faucet on, and I'll get normal pressure for about 30 seconds until it starts to slow and get very slow. After closing the faucet, I can hear the water flowing through the pressure reducing valve for about 10-20 seconds as the system restores back to normal pressure. The low flow indicator on the water meter is behaving oddly. After I run some water and go out to check on it, it slowly turns as the water in the system is restoring back to normal pressure. And then it sort of goes two steps forward and one step back for a minute or two, until it comes to a stop, pauses, backs up, goes forward and repeats. After no water use for 24 hrs, the meter was reading the same, so I don't think there's a leak. But...I am not a plumber, and that's why I'm here to ask for help.

To me, it seems like there's a constriction in the pipe causing low flow, but allowing for the pressure to return given time. That could be something in the pipes (there's no water filter in the house to prevent something coming to the DADU) or the PEX got kinked during the freeze. I dug up the water line that had a lot of exposure and could have frozen, but everything looked fine.

Thanks for reading this far. I appreciate any advice you might have.

 

[GReynolds929]

My first suspect is the PRV, are you able to bypass or remove and test flow?

 

[Sponsor]

 

[Jeff H Young]

possible a prv kinda doubt but dont leave that stone unturned. smashed copper line and problem exasturbated by construction debris , maybe there was damage that wasent fixed. put a pressure guage at the back house (downstream of the new underground line ) Note pressure then flush toilet in the adu and note pressure drop and time it takes to recover. You probebly got rocks dirt debris in that line

 

[Leo_S]

My first suspect is the PRV, are you able to bypass or remove and test flow?

I have valves on either side of the PRV as well as unions, so I think I could figure out a way to bypass by buying a few parts. I'll take a look tomorrow to see if I can do that. Thanks for the idea.

 

[Leo_S]

possible a prv kinda doubt but dont leave that stone unturned. smashed copper line and problem exasturbated by construction debris , maybe there was damage that wasent fixed. put a pressure guage at the back house (downstream of the new underground line ) Note pressure then flush toilet in the adu and note pressure drop and time it takes to recover. You probebly got rocks dirt debris in that line

I'll do the pressure gauge test tomorrow and report what I find. Debris in the line does make sense, but I can't figure how it relates to the freezing weather. I've had the plumbing turned on for probably nine months. In the front house right before the ADU supply leaves the basement, there's a shut off and then a hose bib. I could the close the shut off and then drain out the water from the ADU back to the house to see if that dislodges any debris. Also, I don't see any debris in the clear housing of the water filter in the ADU, but maybe it's too large to make it through the PRV to get to the filter.

 

[Leo_S]

I just had another thought. There was a stand pipe on the water line between the house and the ADU that I kept through construction almost until the end, maybe early fall. It was old and had a corroded galvanized pipe. I was able to unthread it from the copper fitting that was T'd off the line to the ADU. I put a brass cap on that fitting and re-burried it. That was the spot that was closest to the window well and that I was originally afraid had frozen/burst. Now, I'm wondering if that could be the source of debris in the water line and that the freezing/thawing sent a piece of debris from that capped off T down the line to get caught in one of several fittings along the way (from the excavator's repair in ground or inside the ADU) or in my PRV.

 

[Jeff H Young]

Agree none of this relates to freezing weather, youve been running water for many days and report no change, meter dosent spin . So Im leaning away from frozen pipe . I havent dealt much with freezing pipe but it sounded like that has been eliminated .
I suppose feeding hot water through the line would answer that question , Im trusting your report of no spinning meter

 

[Tuttles Revenge]

Most likely is debris in the screen of the PRV or Mechanical shut off. Frozen pipes can loosen debris in the line... We had a frozen pipe at our shop and ended up with a couple small stones in the furthest sink from the main, had to replace 2 faucet cartridges and the angle stop.

If it isn't already, the automated shut off should be after a main physical shut off and the PRV.

 

[Leo_S]

I pulled the PRV and there was nothing in its screen. I attached a pressure gauge to the spigot that's on the same branch as the toilet. It was reading 60 PSI. After flushing, it dropped to 20 PSI where it stayed for about 2 minutes and then started to rise, returning to 60 PSI after another 30 seconds. My next step is to close the shut off in the house basement that feeds the ADU, close the ADU shut off valve and remove the PRV, then remove the cap on the tee that I plugged when I removed the old standpipe (one foot away from the house basement, place a bucket under that to catch what comes out, and open the shut off in the ADU (which is up in a loft space). Hopefully, something comes out and lands in that bucket, but if not I may have to give it a push. I have an air compressor and could blow air down the line. Or I could run a series of hoses from the house about 200 feet to flush that line. One worry is that the debris might not make the turn at the tee and will instead go straight, so I will probably stick make something I can stick down the open end of the tee to block that exit. I might wait for better weather to do this, but I'll probably give up on that since it's Seattle and is planning to rain for the next ten days straight.

 

[Tuttles Revenge]

That sounds like an object in the line. Water pressure will be full, until you open the end and it drops to nothing.. Have you checked that all your main valves or any possible valves between are fully open? I go to customers homes all the time and find their main valves are mostly closed. I agree that there a potential that an object got in the line during repair. Pushing it back is an option.

One time we ended up finding a copper soldered fitting that was manufactured with blockage across most of the tee... almost impossible to locate.

 

[Leo_S]

Most likely is debris in the screen of the PRV or Mechanical shut off. Frozen pipes can loosen debris in the line... We had a frozen pipe at our shop and ended up with a couple small stones in the furthest sink from the main, had to replace 2 faucet cartridges and the angle stop.

If it isn't already, the automated shut off should be after a main physical shut off and the PRV.

I saw your recommendation about the order of the shut off and PRV. Switching now would be tough. My automated shut off is simple to over-ride. It's just a physical shut off with an automated attachment that has a clutch to disengage/over-ride. I wanted that shut off before my whole house filter because about ten years ago I had a filter body spontaneously explode. Luckily, I was home and had a water leak sensor set an alarm off, but it still caused a lot of damage in the 30-60 sec before I had it shut off (I thought it was a smoke alarm at first). I still don't know what caused the filter body to fail--pressure spike, defect, etc. At my home, the water filter comes before the PRV, so a city pressure spike could have happened, but I honestly don't even know if that's a thing. Now, I have automatic shut-offs before the PRV and WHF because I'm still traumatized by that moment when I went downstairs and saw water gushing out.

 

[JohnCT]

I go to customers homes all the time and find their main valves are mostly closed.

I had that at home after servicing my acid neutralizing tank. Seems my ball valve before the tank would corrode internally so the valve wouldn't open all the way even the handle said it was. I replaced the ball valve to fix it, but years later the same problem happened - wouldn't open all the way or shut all the way because the shaft corroded inside the ball.

John

 

[Leo_S]

My first suspect is the PRV, are you able to bypass or remove and test flow?

I haven't figured out an easy way to bypass yet, but I'm gonna give that a try if I don't find debris in the line.

 

[Tuttles Revenge]

I saw your recommendation about the order of the shut off and PRV. Switching now would be tough. My automated shut off is simple to over-ride. It's just a physical shut off with an automated attachment that has a clutch to disengage/over-ride. I wanted that shut off before my whole house filter because about ten years ago I had a filter body spontaneously explode. Luckily, I was home and had a water leak sensor set an alarm off, but it still caused a lot of damage in the 30-60 sec before I had it shut off (I thought it was a smoke alarm at first). I still don't know what caused the filter body to fail--pressure spike, defect, etc. At my home, the water filter comes before the PRV, so a city pressure spike could have happened, but I honestly don't even know if that's a thing. Now, I have automatic shut-offs before the PRV and WHF because I'm still traumatized by that moment when I went downstairs and saw water gushing out.

I just had a manufactures rep in to pitch their new automated shutoff leak detection system and they re-iterated that point of not subjecting the valve to full pressure. Pressure in Seattle can vary from 35psi measured at one of my client/contractors in Wallingford to near 200 at a famous rockstars beach house near Alki requiring 3 PRVs to step the pressure down. Manufactures can and will void warranties based on that installation.

Having already checked the screen, I wonder if the internals of the PRV can't simply be removed rather than bypassing it.

 

[Leo_S]

l thought I would follow up with a message about how dumb it turns out that I am. I spent most of the day doing various tests. I back flushed the main line back to the house. Used compressed air to blow back any debris. Opened up my prv to find nothing unusual. I was drinking a cup of tea deciding where to dig or cut open first. Then, thought I would have a closer look at my water filter. It was completely coated in a nasty brown slurry when I pulled it out. I couldn't tell from looking through the housing. I bet the freeze unleashed a bunch of gross build up in either my old copper pipes or more likely, the city's pipes. Everything works great now. Since my pipes did partially freeze and then transitioned to a clogged filter that was only a couple months old, I never suspected it to be the problem. May others learn from my stupidity.