Serviceability: System Sentryâ„¢ control board features self diagnostics and a hard memory to retain the last five trouble codes, even after power has been interrupted. A 1.5-inch blower door sight glass makes viewing diagnostics simpler. Slide-out blower makes cleaning and service quicker. Accessible igniter and flame sensor help simplify service and inspection. Factory-installed internal trap for vertical installations with built-in cleanout.