Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove the burner assembly from the appliance

Observation:

Visually inspect the front and back of the burner assembly for any restrictions, blockages or damage - pay particular attention to the small metal slots at the back of the burner.
Also inspect the burner cover plate baffle for any restrictions or dirt.
Are the burner and burner cover plate baffle satisfactory?
Notes:
Before reassembly a new burner gasket must be fitted.