I have a 8 yr old Comfortmaker furnace. It started to have problems starting. The only way I can get the furnace to start is by pulling the 2" Pvc pipe on the top of the furnance off. Not, the one attached to the blower. Its the one thats supposed to let air in. Then, all four burners will start. It only does it sometimes tho. A HVAC person says it the wrong size pipe..it should be 3". We have had the pilot cleaned and serviced. Does it sound like the pipe is the wrong size? If so, why didn't it do it any of the 8 yrs we had it before? Thanks Danielle