Diagnosis
Yeah, this one's common. It's usually a dirty temperature sensor (the RTD probe). When it's coated in gunk, it reads the grill temp wrong, so the controller doesn't feed enough pellets to actually heat up.
How to Fix It
Find the thin, pencil-sized metal probe sticking into the grill chamber from the left side wall. Let the grill cool completely, then gently pull it out of its housing. Scrub it clean with a brillo pad or fine steel wool until the metal is shiny. Avoid bending it. Pop it back in and try again.
If That Didn't Work
The other culprit is the fan. Listen during a startup—you should hear a distinct humming. If it's weak or silent, the fan motor might be failing and not pushing enough air to sustain a hot fire. That's a more involved repair.
Heads Up
Don't trust the dial's set temp as gospel. Always use a good standalone meat probe in the cooking area to verify what's actually happening in there. These controllers can be a bit optimistic.