Why a pellet grill's temperature goes up and down

Is a swing of 20 or 30 degrees normal?

Some swing is normal. A bigger swing is a clue, not always a fault.

A pellet grill doesn't hold one temperature the way a gas flame can be turned to a fixed spot. It feeds fuel in small amounts, then waits and watches. One maker compares it to a kitchen oven. The number moves a little above and below, but "the temperature averages out to what you set it to"¹.

That maker says that on a typical, good-weather day, its grill "should fluctuate no more than ±15°F (±9.5°C)"¹. That figure is for that maker's grills. Yours may differ, so check your own manual.

A retailer of pellets puts the line elsewhere. It calls small swings normal, then says you may see swings that "exceed 20-30 degrees," and that's the point where it suggests hunting for a cause². Two sources, two numbers. That's a good reason not to treat any single figure as a rule.

Why does it swing at all?

Think of the grill as a thermostat with a slow fire. Per one encyclopedia entry, pellet grills "use automated fuel and air delivery" to keep a temperature you pick³. A sensor reads the grill's temperature and tells the controller to start or stop the auger when the grill goes over or under a set threshold³.

Pellets take time to burn. So when the controller adds fuel, the heat doesn't jump up at once. And when it stops, the fire doesn't die at once either. The temperature overshoots a little, then comes back. That's the up and down you see on the display.

How the auger, fan and fire pot do this job is on How a pellet grill controls its heat.

What makes the swings bigger?

If the swing is wider than your maker says is normal, look at the usual causes first. One maker lists "frequently opening the lid, cold weather, heavy food load, poor airflow circulation, changing set temp often"¹.

Each of those has a page here:

• Peeking at the food: lid opening and recovery
• Cold air and gusts: wind and cold weather
• Fuel that's damp or crumbly: pellet quality and moisture
• Ash packed into the fire pot: ash and a dirty fire pot

Changing the set temperature again and again is easy to overlook. The grill needs time to catch up after each change, so a hand on the dial can create swings by itself.

When is it a fault?

A part can fail. A source from a pellet seller says plainly that "Malfunctioning parts can be the cause of temperature swings"². Rule out weather, the lid, the pellets and a dirty fire pot first. If swings stay large, ask the maker.

Don't open up electrical parts or rewire anything yourself. Use the troubleshooting steps in your own manual, and contact the maker for anything past those steps.

What should you check first?

Start with the cheap, quick checks. Was the lid open a lot? Was it windy? Are the pellets dry and whole? When was the fire pot last cleaned? The pages above go through each one.

Also look at the number you're comparing. The grill's display and a probe at the food don't read the same spot. That gap is covered in set temperature versus real temperature.