Gas furnace is to draw combustion air from outside. Installation allows compution air to be feed into the furnace from the left or the right and provides a plug for the unused side. With the plug installed furnace tries to run but the pilot light gets blown out. Leaving the plug out the furnace runs fine, but that means it is getting air from within my home. Inlet is per installation instructions. It is not blocked. It is not too long, only ~ 10 ft. Any ideas what is wrong? I have a repairman coming this week but it would be good to have some information for him. Tim

Has this furnace ever worked normally? Or was this something that just started?

It has always acted like this. Tim

If it is installed to the manufactures instructions then it should work. Could be a diverter will have to be fashioned to prevent the direct blast of outside air from hitting the pilot OR there is another problem that has been left uncovered and will have to be visually looked at. Sounds like you did the right thing by calling for On SITE service.