Set temperature versus the real temperature at the food

Why does the dial say one number and my probe say another?

Because they aren't measuring the same place. And neither one is "the" temperature of the grill.

The number you set is a target. The number on the display is what the grill's own sensor reads. Per a pellet seller's page, this sensor is a resistance temperature detector, and the probe "senses the temperature and relays it to the control board"¹. Another source says the sensor "measures the grill temperature and sends the information to the controller"².

Your own thermometer at the grate, or a probe in the meat, sits somewhere else in the cooking chamber. So two working thermometers in different spots can show different numbers.

What does the display actually show?

A live reading, not an average. One maker says its display "shows you the real-time temperature of the grill"³. Over a cook, it says, the temperature averages out.

So if the display drifts above and below your set number, that alone isn't a fault. If you watch the number closely, you'll see it move. The food reacts to the average over time, not to each swing.

Which reading should I trust?

Neither blindly. The display tells you what the controller sees at its sensor, and the controller acts on that. A probe at the food tells you what's happening at the food.

For a cook, the food's own temperature matters most, so a probe in the food is useful. For judging the grill, the grill's reading is what the controller is using. Don't treat a gap between them as proof of a broken sensor.

How to compare them with a second thermometer is a topic for a later page on this site.

Can the sensor itself cause trouble?

Yes. One pellet seller notes that "If you neglect to clean the probe, it could get dirty and start causing your grill temps to fluctuate"¹. That source says to clean it regularly so the reading stays accurate.

How to clean it, and with what, depends on your grill. The manual is the only source to follow here, including its safety notes.

Does food placement matter?

It can. A grill's airflow depends on open space. One maker advises to "ensure at least an inch of clearance" between a pan and the grill's edge³. Blocking airflow can disturb temperatures, so crowded food or a large pan can leave the display and the food telling different stories.

What should I do with a gap?

Note it, don't chase it. Cook by the food's own temperature, and follow safe-temperature numbers only from an official food-safety source, not from the grill's dial.

If the gap is large and you can't explain it with the lid, wind, pellets or a dirty fire pot, follow your manual and contact the maker. Other causes of wide swings are in why a pellet grill's temperature goes up and down.