I have a Trane XE90 natural gas furnace. When heat is called for, the Power Vent Fan starts, the ignitor goes on and turns orange, I hear a click calling for the gas, but the furnace does not light. After the furnace fails to ignite, the unit continues to operate as though it had ignited and blows cold air throughout the house. However, if I gently blow toward the ignitor after it turns orange, the furnace lights up and warm air is forced through the system. I attempted to troubleshoot the problem by performing the following steps. First, I removed the front metal panels and cleaned the inside of the furnace to remove any dust and other collected particles in the unit. Next, I replaced the air filter with a brand new filter. This failed to solve the issue. Next, I replaced the ignitor, but the unit still failed to ignite without the gentle blowing. I then checked the tubing going to the pressure switch and the entire exhaust line for obstructions. I was unable to find any obstructions in either line. Finally, I reset the entire unit following the instructions listed on the furnace panel. This too failed to solve the issue. I do not want to run to my basement and blow through the grate in the furnace panel every time my thermostat calls for heat. Can you please help me resolve this issue.