The switch uses a bi-metal strip to 'ping' a contact open and shut to get a clean electrical make and break.

The contact resting on its back-stop with clearance to the internal part of the spade connection. When I opened up mine it was pinging back and fore OK but not always making a good contact, even the low current of the relay is enough to cause some arcing at the contacts due to the relay inductance and back-emf. I tried cleaning the contact surfaces, but there is very little room, and by the time I had finished it was no longer pinging back and fore. I'd already bought and fitted the Burlen replacement by this time, this exercise was just out of interest.