Yeah that would have been my first thought aswell....replace the thermostats
Here is a link so you know what they look like...make sure you have a read about how to replace them
http://www.partmaster.co.uk/cgi-bin/product.pl?PID=530751&query=White%20Knight%20CL432W&model=CL432W&path=67146,110718:67149
res1492
September 2009