Diagnosis
Sluggish heating is almost always a fuel flow problem. The usual suspects are a tripped regulator (see the temperature question), a nearly empty propane tank, or clogged burner ports restricting the flame size.
How to Fix It
First, perform the full regulator reset procedure described earlier. If that doesn't restore strong blue flames, check your propane tank level. Swap in a full tank as a test. If you still have weak flames, your burner tubes likely need the cleaning procedure—clogged ports mean less gas is being combusted, so less heat is generated.
If That Didn't Work
Check the venturi tubes—the parts that mix air and gas right behind the control knobs. Make sure they are fully seated into the control valves and that the air shutters (little metal flaps on the tubes) aren't blocked. An improper air mix can lead to lazy, inefficient flames.
Heads Up
Weigh your propane tank. A standard 20 lb tank weighs about 38 lbs when full and 18 lbs when empty. If you're below 25 lbs, you're running on fumes for high-heat cooking. Cold weather also reduces tank pressure, making heating slower.