I have a sewer type odor around my furnace (I have posted about this before). Ive had 2 plumbers and 1 HVAC tech come out to determine if this is propane or sewer gas. It has been determined that there is no propane leak. We thought we had the problem solved when we cleaned a trap into which the condensate line drained. But the problem has returned. Today I removed the above floor trap (it was cut in to a 3" stack next to my furnace with a 2" tap. I removed it and capped off the 2" portion of the wye. I then ran new drain lines from the furnace condesate trap to a floor drain, everything has plenty of fall and the water runs out the pipe when the furnace runs.

Here's my questions - how does the furnace condensate "trap" stop gases from entering the drain pipe? The tap is a small white box about 2"x4" by 1/2" . Has 3 lines into the top. 2 appear to be water drain lines the other some kind of small line maybe determining if the trap is full before the gas valve is opened? A flexible drain line comes from the front of this trap about 1 1/2" from the bottom and the goes on into my new drain line. Is there tubes in this trap that form a p trap? How does it stop the gases from entering the drain line and then into my basement? If I add another regular p trap in my new line will that have any negative effect on the operation of the furnace (I'm worried about the line which goes to the gas valve switch from the furnace trap. Please help as I've had this odor problem on and off for over 2 years.

 

Is one of the pipes an opened vent pipe? If it is, there is something called pro-vent that you can put on the end of that pipe.

If not, can you post some pic to photobucket.com ?