Spinflo 5500 Intergrill Cooker

Hi folks. I have a problem with the flow of gas to the grill / oven burner on the Spinflo 5500 cooker fitted to our Symbol. This has only arisen in the past two weeks. Instead of a controllable flame from the burner we have a swirling flame which cannot be adjusted. Also the flame is extinguished after a few minutes. Upon inspection the only thing I notice is that the control knob is not working the same way as those for the hob burners (which are working fine). The grill / oven control knob is not popping back out after depressing it for the ignition process. I have removed the actual plastic knob and depressed the mechanism by hand and observe the same issue. So it’s not the actual plastic knob at fault. Any ideas on how to correct this myself or do I need to take the van in to have the cooker serviced ? I am nervous of doing anything to affect the operation and safety of the unit. Thanks in anticipation of the usual support

Just to close off this case. Was able to resolve problem with the control knob. Removed the plastic knob itself (just pulls off) and cleaned / oiled the 'spindle'. Now seems fine fingers crossed