Oatey Cast Iron Toilet Flange Replacement Product #43539 Too Narrow?

[Barry]

I installed an Oatey replacement flange in a 4" cast iron pipe about 10 years ago. Ever since, the residents have had periodic issues with blocked toilet. Plunger usually works to clear. Last month plunger didn't work, seemed their might be an object jammed in the trap, so I replaced toilet with an Eljer Diplomat. Today, another complaint of backup.
I'm trying to figure out what could be causing these regular blockages.
This replacement flange uses internal Stainless screws to secure the flange to the interior of the cast iron pipe. Could the narrowing of the pipe from 4" to 3" make it more likely to cause blockage?
As an alternative replacement flange, is there a secure method / product to secure a new flange without narrowing the pipe?
Could a vent problem cause these periodic backups?
Could a blockage in the main stack or in the horizontal line to sewer cause the toilet to backup?
Thanks for any thoughts on this.

 

[Jeff H Young]

are you 100 percent sure there is no issue below the flange ? I dont think its the flange , could be thier bathroom habits, could be the toilets , could be a mainline stoppage

 

[Sponsor]

 

[Barry]

No not absolutely sure. I continue to have the issue with the new toilet, so probably not the toilet, and more likely the main line or the vent.

If it happens again would it make sense (after clearing the toilet) to pull the toilet and run a snake from the 2nd floor toilet flange down to the sewer? It's less than 100', so it is doable.

 

[Reach4]

I would consider hiring out the snaking with the big machine to a drain cleaning specialist. The big machine can be dangerous.

Plunging into clog near but below the flange can blow out the wax seal. A closet auger can clear a clog in the trapway and for a bit below the flange, without danger of blowing out the wax.