How can I fix my Cannon Chesterfield top oven and grill?

Model No: C60GCW
Serial No: 708140086

Although the ignition works fine, both grill and oven flames seem to cut themselves after 30 secs of less.
I have checked timer setting as manual suggests but no luck!

I bought this cooker 2nd hand only this summer and everything worked fine. I like Cannon but I am not in Warranty and would love to be able to fix it myself before paying call out charges.

Thank you for any help.