Smeg A1.1 cooker replacement thermocouples don't fit! ?

Our Smeg A1.1 has had flame cutting out problems for ages now, couldn't afford to have it fixed till recently, but... our engineer guy keeps coming out with the new thermocouples and they don't fit! It's been twice now, all the parts come from Smeg themselves but just are the wrong size, apparently having been 'redesigned' in the intervening years. Anyone else have this problem? Maybe you know the parts we actually need, as opposed to what Smeg says... Our engineer is as frustrated as we are, but at least he doesn't have to stay in all day...