Diplomat 600 Ga ?

I have a Diplomat 600 Ga gas oven that I have difficulty with when switching it on, the gas & ignition seem to struggle to work together, once it has finally lit due to opening & closing the door to ensure it is fully lit, it then appears to overheat, the regulator screen fogs up & a safety devise must kick in turning the oven off altogether.
After approx 20 mins (I presume once its had chance to cool down) the clock LCD reappears flashing zero's, I reset the clock & it will allow me to use the oven again for another short period of time before it happens over again.
Does anyone have any answers to this problem as this site seems to have plenty of questions on this issue but doesn't appear to have any relevent resolves.
Help please