Damp or poor pellets and what they do to heat

Can the pellets themselves cause uneven temperatures?

Yes, according to several makers and sellers. The fuel is the first thing to rule out, since it's cheap to check.

One maker states it flatly: "Low-quality or old pellets can cause temperature fluctuations"¹. A pellet seller describes a controller set to 250°F while the grill drops to 200°F, then climbs to 325°F². That's a very big swing. Many other things can cause one, so the pellets are only a suspect.

What does a poor pellet do?

The sellers point to ash. The same seller says the culprit is often "a cheap, low-quality brand that produces excessive ash"². Its page says too much ash makes it "hard to hold a steady temperature" and can cut the oxygen to the fire².

Another page from the same seller adds that bad pellets "can interfere with these sensors by creating excess ash"³. So the grill may not read the heat the way it should.

That seller makes pellets, so it has a stake in this advice. A grill maker's own cleaning help also ties ash to swings. It's covered in the page on fire pot cleaning.

How can I tell if a pellet is bad?

Look and listen. One maker says to check pellets for a sheen and a clean snap when you break one. Then comes the rule: "If the pellets crumble or look dull, try a fresh bag of pellets"¹.

A pellet seller says the same in its own words: good pellets have a nice sheen and make a snapping sound when broken³.

What about damp pellets?

Damp pellets are a known risk, and humid air makes it likelier. A grill maker's help page warns that in very humid conditions, "leaving pellets sitting in the hopper for even a couple of weeks could be an issue"⁴. You'd see it, it says, "if they struggle to reach the desired temperature or the fire goes out"⁴.

That page also gives the same maker's remedy for a grill that won't be used for a while: scoop the remaining pellets out of the hopper. Follow the steps in your own manual rather than copying these, since hoppers and guards differ.

I found no source here that gives a moisture percentage or a test for dampness. So there's no number to quote. The sheen-and-snap check above is what the sources offer.

What should I do about it?

• Look at a few pellets before a long cook.
• Swap to a fresh bag if they're dull or crumbly.
• Don't leave pellets sitting in the hopper for weeks, especially in humid weather.
• Check your manual for how it says to store pellets.
• Clean ash out of the grill on the schedule your manual gives.

If the grill won't light or keeps going out, follow your manual's troubleshooting steps and contact the maker.

For the wider picture of what else moves the temperature, start with the overview of temperature swings.