The part(s) or condition(s) listed below for the symptom Gas stove burner not heating properly are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.
If a burner flame is not changing as expected when the burner valve control knob is turned from low to high, it's possible the knob is stripped out or damaged and unable to rotate the valve stem. Inspect the knob for any cracks or wear and replace if necessary.
If a burner flame is not changing as expected when the surface burner valve control knob is turned from low to high, it's possible the burner valve stem is damaged and not actuating the valve appropriately. If the valve stem appears loose or wiggles you should replace the surface burner valve.
The burner cap helps to distribute the gas evenly around the burner. If the cap is damaged or warped the flame can be higher on one side than the other. Inspect the burner cap for damage and replace it if necessary.
For best cooking performance use a burner that is best suited for the size of cookware being used. Using cookware that is too small or too large for the burner is not recommended.