Symptoms: Stove goes into "Igniting" mode and starts a fire, but will stop feeding pellets shortly after the room blower fan engages and the panel shows "Heating" mode.
Resolution: This video shows common symptoms, causes, and resolutions related to the vacuum switch: https://www.youtube.com/watch?v=a0mVStSjD7U
Tapping on the housing to dislodge a stuck diaphragm, adjusting the vacuum switch sensitivity, and doing a deep cleaning of the pellet stove are common solutions that will often resolve the issue.
Cause: The vacuum switch has an internal diaphragm that will engage when the exhaust fan runs and creates a negative pressure (or vacuum) in the main chamber. Sometimes the diaphragm will get stuck, causing the switch to not engage. Agitating it, by tapping on the switch housing, will often dislodge it and it will resume working.
Another common problem that happens, is when the stove's internal exhaust chambers become clogged with soot and ash, causing an airflow restriction. A good cleaning should eliminate this problem.
Negative pressure leakage can also cause a vacuum switch to not engage properly. This occurs when the stove draws in air in a place that is unintended, such as through a gapped front door gasket seal, or loose ash pan drawer.
This video showcases the 2 types of airflow problems; restrictions, and leakages: https://www.youtube.com/watch?v=F_TqV6mddJ0
If your switch has a sensitivity adjustment knob, it may require a periodic adjustment. Rotating the knob counter clockwise by 1/4 to 1/2 turn usually resolves any settling of the internal spring and takes some of the tension off of the internal diaphragm.