When you say main vent and ice, would this have anything to do with the vent in the attic. I don't understand how heat and ice would come together on the same vent. I am a total lay person. I had a plumber who went in the attic to run a snake, he said it was because the air flow was blocked to the sewer line and that is why the toilet had a bubble sound after flushing and the line that ran from the sink and toilet to the main was blocked. Could this be the same main vent that you refer to and could it have been cracked by snaking it? Also, is this a common practice to run a snake up in the attic. I surely did not go up there with him... yucky attic.

Its very common to snake out a sewer line vent stack. That can get filled with snow and ice and stop the drainage. Tree debris and leaves/ pine needles can clog it.

The attic part is confusing hear unless someone for some odd reason put a y in the stack and a clean out.
Normally you have to get on the roof
Some times you can use a hair dryer to thaw out a vent stack the froze. But if it still has debris in it then it can freeze back up easily.

Its possible to crack a vent pipe I never did it yet. If enough water frozen in the vent and that could crack it .

The snake in the pipe sounds like its tearing up the pipe but the snake really isn't that powerful It more will break than anything else if it gets to snagged.

If there is sewer gas smell their know I would bet it was from frozen water and a expanded pipe and a snake may crack it but again I never heard of it yet.

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