Where's the Reset Button?

My HJA 5100 range cooker has done less than 12 months work and both the fan assisted oven and the grill have stopped working. I have had the cooker since December 2007 but it was in storage until last August. It stopped working in February this year (2010) after only 6 months use.

I have tried to get Leisure (manufacturer) and Howdens (supplier) to fix this. Neither of them will take resposibility. I therefore have had 2 independant engineers out to look at this problem and they both think it is the Thermast Reset which has tripped. How can the engineer reset this?