Thanks for the question, that's a good one to ask for sure.
Our technician would ask if the pilot light is staying lit. Technically, the only way to check if a thermocouple is working is to hook a volt meter up and set it to millivolts. This should let you know if the thermocouple is actually opening the gas valve.
I realize these aren't the most detailed of instructions, so for a more thorough explanation of how thermocouples work (and how best to determine if yours is working) please give us a call at 1-888-388-6372. A member of our Tundra Restaurant Supply team would be happy to talk through the details with you.
Answered on 1/28/2013 by Andrew Call from Boulder, CO