Switflow 75, SIT- How to fix it?

Dear sirs,
My boiler central heating function is broken. When I turn it on, the pilot light increases and the boiler works for 10 minutes and then cuts out. It would seem that there is no temperature control and the cutout is activated?

I have been told it is either a thermistor or a circuit board problem- could any kind persons tell me what they think it is and how I go about fixing it?

Best Regards
Nick