Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Remove the burner

Observation:

Inspect burner for damage and good general condition, also ensure burner baffle is secure and not become detached.
Even if the burner looks in good condition it could still be restricted/partially blocked.
The best way to confirm this is to shine a torch up through the burner, if it is clear then light will be clearly visible when looking through the baffles (as shown in the photo)
Note:
1. Ensure that when removed care is taken not to damage the ceramic face of the burner.
2. Before refitting the burner inspect the sealing gasket and replace if damaged.