Diagnosing & Clearing Blocked Plumbing Vents

Although possibly the most common cause of a slow moving or backed up drain is a clogged pipe, the problem can also be the result of blocked plumbing vent. This vent sits on top of the roof of your home and circulates air into the pipes to prevent them from vacuum sealing closed in a way similar to what happens when you cover one end of a full straw when water flows through. Here's how to determine if your plumbing vent is clogged and how to clear it.

Determine if the Vent Is Actually Blocked

Leaves, trash, nesting birds, dead animals, and other debris are some of the things that can find their way into plumbing vents and cause blockages. Plumbing vents on homes in cold climates are sometimes blocked by ice. Vents have also been known to rust and collapse internally.

Regardless of the cause, there are several telltale signs the cause of your slow or backed up drain is the plumbing vent. These include:

  • Gurgling sounds: When the pipes are unable to get air from the plumbing vent, they suck it in through the P-Traps. Thus, you'll hear a gurgling sound around the drain openings. The toilet will also gurgle and sputter each time you flush it because it needs air to fight the pressure caused by the rushing water.
  • Slow draining: Water drainage will slow to a crawl or cease completely because there is a greater amount of negative pressure in the pipes. Plunging, snaking drains, or using chemicals don't seem to help eliminate the blockage. More than one drain may be affected at a time.
  • Strong odor: If the blockage is severe enough, a strong odor may fill the home due to water draining from traps that were designed to prevent sewer gases from leaking into the house. The odor may also come from deceased animals clogging the plumbing vent. In either case, the vent has to be unclogged immediately.

You can manually confirm the plumbing vent is clogged in a few ways. You'll have to climb onto the roof, so make sure you have a partner who can steady the ladder and generally help ensure you stay safe while up there.

Once on the roof, try one of these three methods for confirming a block:

  • Use an inspection camera to look inside the vent pipe for the clog.
  • Use an extra-long plumbing snake (at least about 10 to 20 feet) to explore the pipe. If you hit a block, then you've got a clog. Try to pull out a sample using the snake to see what the blockage may be.
  • Fill the vent pipe with water using a garden hose. If the water backs up in the pipe, you've got a clog.

Clearing Blocked Vents

Eliminating a blockage in a plumbing vent is pretty simple, but it will probably require quite a bit of elbow grease depending on how thick the clog is. To perform this task, you'll need a plumbing snake, a garden hose with a variable speed nozzle, and a garbage bag for any refuse you pull out of the vent.

  • Start by setting the nozzle to full force and spray the inside of the vent. Many times this will be enough to dislodge the clog, especially if it's only leaves or trash stuck in there.
  • If the water backs up instead, then you'll need to get more aggressive. Use the plumbing auger to either poke holes in the clog or hook the clogging element and pull it out. Be prepared. It could be a dead animal, so you may want to have someone else do it if you don't have the stomach for it.
  • Alternate between using the garden hose and the snake until the water drains easily or it feels like the clog has worked itself loose.
  • To avoid getting clogs in the future, be certain to fit your plumbing vent with a compatible cap. You can usually purchase them at home improvement stores.
  • If the clog is caused by ice, simply pour hot water down the plumbing vent until it melts.
  • A plumbing vent that has internally collapsed because of rust will need to be completely replaced by a plumber.

If you're not comfortable trying to eliminate the clog yourself or your drains continues to run slow even after clearing the vent, contact a company like A Absolute Plumbing & Heating for assistance.