DIAGNOSIS The grill is experiencing extreme temperature instability. Primary cause is a dirty or faulty RTD temperature probe. Secondary cause is poor pellet quality or feed rate issues.
FIX Clean the RTD probe. Unplug the grill and let it cool. Remove the cooking grates and heat baffle. Locate the thin, metal, pencil-like probe extending into the left side of the cooking chamber. Scrub it thoroughly with a brass brush or fine steel wool to remove all carbonized grease and soot. Do not bend it.
IF THAT DIDN'T WORK Calibrate the controller's temperature offset. With the grill clean and at room temperature, power it on. Press and hold the PROBE and POWER buttons simultaneously for 3 seconds. Use the up/down arrows to adjust the offset in ±25°F increments. Start with a +25°F adjustment if the grill reads low. Confirm with a reliable third-party oven thermometer placed on the grate.
HEADS UP Massive swings often indicate the P-setting may have been altered inadvertently. On the SMOKE setting, pressing the TEMP UP button cycles through P-settings (P0 to P7). Lower numbers (P0, P1) increase pellet feed for more heat and less smoke. Higher numbers (P6, P7) decrease feed for more smoke and less heat. For stable temps at 225°F+, use P-setting 4 or lower.