Upon arrival I was told that right side of building wasn’t heating. Set up ladder and went to attic crawl space to find resettable Limit that was just replaced In the tripped position. Reset and checked operation. Found flue pipe not heating up at all, can feel cold air blowing in and furnace exhaust is venting out of the side where Limit switch is located, causing it to trip. Watched as Limit tripped and temp probe read 150 degrees. Shut down Reznor furnace and removed flue pipe completely from unit. Found no restrictions at all so I put back into place. Returned power to Reznor furnace and ran heat. Limit switch temp never reached higher than 75 degrees and flue pipe exhausting normally. Let system cycle 5 times and system is operating normally. Called Reznor because we have an intermittent negative draft causing vent switch to trip. Per Reznor, they suggest we install a power vent (CA1-115V, PN: 136959) onto system. Uploading quote.