Hi, my name is ***** ***** I will look to assist you with your query.
The oven has the following elements:
– Bottom element 1400 W
– Top element 1000 W
– Grill element 2000 W
– Circular element 2500 W
Could it be possible the Top and Bottom elements have failed and only the circular element working, hence why the oven only heats up on Fan?
If your happy the elements are working, it could be a control board or control switch failure.
As you have suggested the thermostat knob is shorting, it could also well be the debris in the thermostat knob is also in the control knob and stopping the other elements from working.
The control knobs are accessed by removing the hob which reveals the top of the oven, this can be fiddly.
Since you have multiple faults the fact you need to interfere with the gas hob to get to the faulty components and there being a fair bit of troubleshooting, I would suggest you get out a gas safe registered engineer.
Please let me know if you require any further information or clarification.