Belling Gas Oven flame problem

[Rastanking]

Hi everyone,

I wonder if anyone could help me with this problem. I have a Belling single Gas Oven and when I light the oven the flame rises then falls away to almost nothing, the grill works fine as well as the hob, which is on the same supply.

Is this something to do with the timer as my grandson has been playing with it or something else?

Thanks in advance

Andy