Oven Fault Diplomat ADP0150

We are having problems with a diplomat gas oven ADP0150.
The oven and grill do not seem burn correctly when first lit until the oven has been on a while (and presumably reached specific temperature).
The grill burns with an uneven flame until the appliance has warmed up and the oven keeps trying to re-ignite (even though the flame has not gone out).
The cooling fan was recently replaced as this was initially thought to be the problem. The oven gets condensation behind the display panels which again clears once the oven has been on a while. The area above the oven door also gets very hot initially. This is why the fan was suspected as being problematic as once the oven has been on a while and you can hear the fan running at a higher speed then the problems stop.
Two engineers have looked at the appliance and said it is not a gas problem and suspect the issue is electrical but replacing the cooling fan has not solved the problem.
I wonder if there is a sensor or control that decides what speed the fan should run at and this is not working at the correct temperature?
Any advice or help welcome otherwise we will have to replace the appliance as we cannot find anyone local able to fix the fault.
Thanks