Can anyone tell me what the possible problem is which results in the gas oven flame decreasing to its minimum level (to a degree where I am unable to cook food) when I close the oven door? If I open the door, the gas level increases again? I have been told its the thermostat but I’d like to check first. If it is the thermostat, is it easy to replace on this BEKO model? Any advice would be appreciated. Thank you.