Pellet Grill Temperature Swings Far From the Set Point

What it
usually means.

A pellet grill holds heat by feedback: the controller reads a probe inside the chamber, compares it with the set point and adjusts how often the auger drops pellets and how hard the fan blows. Some swing is built in, especially on older controllers that run fixed cycles; newer PID controllers hold closer. Large or new swings come from something upsetting that loop. The chamber probe, a thin rod on the inside wall, reads wrong once it is coated with grease and smoke. Ash left in the firepot smothers the fire, which starves and then catches again in a rush. Pellets that are damp, dusty or of mixed length burn unevenly. Wind, rain and cold pull heat from a thin chamber, and each lid opening throws the count off. A combustion fan slowing on worn bearings or clogged with ash, or an auger that feeds in fits, makes the fire rise and fall. A flameout, where the fire goes out while the controller keeps feeding, can fill the pot with unlit pellets that later light all at once, so a grill that lost its fire is switched off and left to cool before any restart.