can't remember now when they changed the heat exchanger design. I used to know. But its easy to tell from the shape of it. From a side profile of the heat exchanger the old one is flat down the front and the new design concaves slightly like a shapely woman. If its the earlier one probably you need a new heat exchanger to cure the problem.
Thinks "Swiss Tony" - Lucky me, mines like a shapely woman Just (another) new electrode is going to fix this - now I can see where the electrode is arcing through the ceramic to the metal base. "Made in Italy" is stamped on the part. Maybe a clue as to why the spark goes off prematurely?