Flush Creates Pressure on AAV (so no vent)

Users who are viewing this thread

plumbdumber

New Member
Messages
2
Reaction score
0
Points
1
Location
Beachwood, Ohio
I have recently became the proud owner of a gutted and renovated old home. I *think* the basement bathroom is totally new. Everything worked great until I used the shower a few weeks after moving in. After the shower, the toilet wouldn't flush - just fill the bowl to the top and slowly drain. When I removed the P-trap on the sink, the toilet worked great. I knew I had a vent problem and figured the shower trap was dry so my home inspector missed it and didn't test the shower.

I couldn't find a vent pipe from the corner of the basement to the stack. Just to be sure I climbed on the roof and snaked both vents with a 50' snake. Of course the damn snake wasn't anchored in the hand crank housing and I lost it down the main stack. The (cast iron) cleanout was half buried in the concrete floor of the basement foundation (old house). I pulled the toilet just above the buried clean out and retrieved the snake using a second snake in which I modified the tip (made a spiral hook). Both snakes came out dry. I am now confident the vents and ~20' of the main sewer are clean (the retriever snake was 25' long and I hooked it at full depth).

I called the renovator and was told the bathroom used two AAVs. Please don't tell me I need to vent them to the roof...I don't like them at all but there's no easy way to do this - the bathroom should have been on the other side of the basement. I checked and all permit's and inspections were in place. I can't believe they approved AAVs without access but that's the situation. I cut the drywall and exposed both AAVs. If I remove either one, toilet flushes great. I bought a new one for swap troubleshooting and nothing changes. Holding a baggie over either AAV stack shows air pressure (the baggie fills when the toilet is flushed). I understand the problem - pressure builds in front of the flow during a flush. Both AAVs see the pressure but it's never relieved. Since neither AAV sees the vacuum, they never open. With either AAV removed (so that the pressure can pass) the toilet flushes amazingly well.

I'm thinking a clog of some type is keeping the pressure from being relieved via the main stack vented in the roof. However, this would mean that the clog has to be between the bathroom and the main stack which is 20' away. If I had a clog withing 20' of a 4" pipe, I would expect things to be backed up to the toilet or shower by now. If the clog is after where the bathroom hits the main sewer line heading out of the house, the toilet would be able to vent the pressure via the main stack, unless the connection joint is under water because of a clog. However, this should also create a sewage backup into the new bathroom after about 20 flushes since the connection appears to be right where the main stack goes into the basement floor (I can see where the concrete was replaced). The house has 3 other bathrooms on the first and second floors with no issues.

Two questions:
1) Is it time to pull the basement toilet and snake, or dig out the main cleanout and have roto rooter clean out to the neighborhood sewer line? (I've already taken a chisel to the concrete to access the plug but I don't think it's been removed in 50+ years so it may be a drill it out and replace with a new brass plug job).

2) Can I put an accumulator/cylinder/chamber next to an AAV to absorb the pressure pulse and let the AAV's vent? When I tee a large zip lock off the AAV it actually works - the bag fills then goes down as the AAV opens. This is telling me something - the volume to absorb the pulse is small so any clog must be near? Do such pressure absorbing devices exist? Would this just be masking a problem that will blow up some day in the future?

Thanks in advance!
 
Last edited:

hj

Master Plumber
Messages
33,600
Reaction score
1,037
Points
113
Location
Cave Creek, Arizona
Website
www.terrylove.com
There is NOT enough pressure in the line to actuate ANY "accumulator" device. Your problem is some type of restriction in the line BEFORE it reaches the main line.
 

plumbdumber

New Member
Messages
2
Reaction score
0
Points
1
Location
Beachwood, Ohio
There is NOT enough pressure in the line to actuate ANY "accumulator" device. Your problem is some type of restriction in the line BEFORE it reaches the main line.
Thanks HJ. Sounds like you definitely recommend pulling the toilet and snaking to the main line. I snaked through the sink trap next to the toilet and found nothing. I guess their could be a restriction prior to meeting the sink drain or in the toilet trap. Either way, it looks like pull the toilet and check both sides (toilet and drain).
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks