I believe there should be two thermostatic switches - one turns on / off the heating element to maintain temperature and the other is an over temperature trip. Once the over temperature trip goes it needs replacing as it is non resettable - usually identified by either a green or blus spot on the actual thermostat.
So if you only found one thermostat then you've one more to find - generally right beside the heating element. If either fails then both should be replaced as a pair. Cost for pair is usually around 20 pounds.
Gram
March 2010