Should one or more of the gas cooker rings not ignite, we recommend you check that the burners themselves are free from fibre or strands of a cleaning pad, simply remove the burner caps and wipe around the burner rings with a dry lint free cloth then re-try. If you have a glass lid fitted to your appliance, ensure that it is fully upright and free from any obstructions as either of these conditions will result in the gas supply to the hotplates being shut off until the problem is resolved.
If the problem persists, ensure that the batteries (where fitted) are new, or if the cooker/hob has a plug, check the socket is working and try a new fuse.