The thermal fuse located near the heater is bad and you will need to replace it. it is part number LA-1053, You can order this part at the following locations online... http://www.apwagner.com/, or http://www.repairclinic.com/, or http://www.partstore.com/. All 3 of these places are a good place to order your parts because of thier liberal return policy....
it is item 5 in the diagram
Thanks for the quick reply. Sounds like something for a technician to handle for us - we're not particularly handy. I appreciate knowing what we should expect, however.