Ash buildup and a dirty fire pot

Could a dirty fire pot be behind my swings?

It can be. The fire pot is the small cup where pellets burn, and ash collects in it as you cook.

A grill maker's help page says what too much ash can do. Without regular vacuuming, "the fire cannot light and burn properly"¹. With too much ash, "the fire can easily go out mid cook resulting in temperature drops and spikes"¹. A pellet seller makes a related point about ash in general. Too much of it can snuff "out the oxygen supply to the fire"². Another of its pages adds that a clean grill "will help maintain adequate airflow," which keeps temperatures more regulated³.

How often does it need cleaning?

It depends on the grill and the pellets, so there's no single answer. The Z Grills help page gives two different intervals. Its cleaning summary says to "Vacuum out the fire-pot and grilling area (every 5-10 hours of operation)"¹. Further down, it says that, depending on the pellets, "the ash may need to be clean out every 10-20 hours of operation"¹. That's the maker's guidance for its own grills, sold in Australia.

Your manual may give a different interval, or may say to clean after every cook. Use your own manual's interval.

What does the manual say to do?

I can't tell you what your manual says, because each one differs. What I can say is what this one maker's page says, as an example of the pattern.

The page tells owners to vacuum the ash out, and to do it "Once the grill has cooled down"¹. It also tells owners to check for packed ash around the ignition rod, the part that lights the pellets, and to clear it¹.

Your manual lists the exact order, which parts to lift out, and which tool to use. Follow it for your own model, including every safety step it gives. Follow your manual's safety steps for the whole job, from start to finish.

What else builds up?

Grease. A pellet seller warns that a dirty grill can mean "excess grease and ash buildup"³. That's a separate job from the fire pot; follow your manual for it.

Will a clean pot fix my swings?

Maybe, maybe not. Ash is one cause among several. A clean pot won't help if the real problem is a windy spot, a lid opened every few minutes, or damp fuel. Work through the weather page, lid opening and pellet quality too.

If the pot is clean, the pellets are dry, and the swings continue, the next stop is your manual's troubleshooting section and then the maker. A worn part can also be at fault, and that's for the maker or a qualified repairer, not for a home fix.