Problems with my Stove gas oven GL616 Lighting up when first turned on?

I have a Stoves gas oven GL616 oven. It is approx 4 years old. When i turned it on i can hear the click as it tries to light the flame. It seems to light and then when you close the oven door the flame goes out and you can hear clicking again as it tries to light again. There is a slight smell of gas. Eventually it stays alight.

This only seems to happen at the begining when you turn the oven on. Once it has been alight for a while it seems okay.

I have had the gas engineer in and he replaced the burner but the problem still seems to be there.

As anyone any ideas what the problem might be? The gas hob above the cooker is okay.

The next time the gas engineer comes perhaps i can suggest some possible reasons to him?

Many thanks for your help.