Your friend Joes advice will fix a clogged pressure switch problem that happens sometimes but make sure if you do that fix it don't blow towards the pressure switch if you do it will ruin the paper like material inside the switch and then that part will need to be replaced for sure. Most minor problems I come across are high limit cut outs from dirty air filters, also too many air vents shut or blocked. The second is from a failed sensor flame signal caused by soot on the sensor or no flame of course. If the small inducer motor starts up and you here a "click" from the gas valve and u smell gas for a sec u got a bad igniter it will try three times then turn the main fan blower motor on until it's rebooted (turned off and on) Call or text me if u still need help 913-634-3307gormanshvac.com