Hi dan,
I really need a model number to give specific help. However, these are normally located just above the heater element which is behind the rear cover of the machine. A case of removing about a dozen screws. The thermostats come as a kit (two of them) and both need replacing. You can order spares from us here:
www.ukapplianceparts.com
If you cannot find the part contact me via the site for more details.
Lee
December 2006