Plumbing Vent Cover

Ade lives in cold and snowy Chicago, IL. All of a sudden his plumbing fixtures stopped working correctly. Here's his story:

"I had a leak around my plumbing vent repaired last year and the roofer put a cap (see picture) on the vent.

I started having problems with my 2nd floor toilet and later with both 3rd floor toilets.  Then around Christmas my kitchen sink would not drain.

I did some research and found out about vent pipes freezing which proved to be right 'cause as soon as it got warmer the sink was fine again.  I never had this happen before even in weather much worse.

It got me thinking about the repair that was done to the vent and I realized that enough air might not be coming into vent because of the cap. Could this affect the performance of the vent?"

Here's my answer:

Ade, you bet the cap and the flashing that's on there were the source of the problem.

Plumbing vents need to be unobstructed. My guess is that the underside of the metal cap RAPIDLY became choked with ice as your plumbing vents are normally aspirating moist air when nothing is going down your drain pipes. At some point, the ice came in contact with the top of the vent pipe and no air could ENTER the vent.

When you flush a toilet, then the vent SUCKED air from the atmosphere to replace the air in the drain pipes that's being pushed ahead down the drain by the rushing water and waste.

Get rid of the cap and all your troubles will disappear.