This could be caused by one of two issues:
1) The first being that the orifices need to be cleaned. To access the orifices you will need to remove the dual ring burner and insert a small pin into each orifice or remove to ensure that they are clear from any food, spider or residue debris.
2) The second issue could be the regulator being in a lock out state or has failed internally. To reset the regulator, disconnect from the LP tank for a period of about 5 minutes then reconnect and turn the fuel on slowly.
Please refer to our troubleshooting video at the link below for more info.