Troubleshooting Diedrich Roaster Thermocouple or High Limit failure

Problem: Roaster Thermocouple or High Limit failure

Taken from the old Diedrich web site, which has been replaced and I could not find this.Resolution:  If the Diedrich roasters flame goes out and can be relit by resetting it; locate the Watlow high-limit. It is a small, black plastic molded box approximately 4 inch x 2.75 inch. In a manual roaster, it is located behind the switches in the electrical box. In an automated roaster, it is in the automation lectern.
Troubleshooting Diedrich Roaster Thermocouple or High Limit failure

Tools Needed: 

  • Electrical jumpers
  • Voltage meter
  • Flat head screwdriver
  • Phillips head screwdriver


REMOVE the red and yellow wires that are attached to the thermocouple terminals. Place a jumper or loop between the TC (+) and TC (-) on the high limit in place of the wires. If the roaster lights and stays lit, the cause is either a bad thermocouple or a loose connection between the thermocouple and the high limit. Check the connections before replacing the thermocouple.If the roaster continues as before, goes out but relights upon resetting now you ll need to check the high limit.Find the normally open or NO terminal and common or COM terminal. Put a jumper between those 2 terminals WITH the wires in place. If the roaster now stays lit the high limit has failed and needs to be replaced.WARNING! Remember that this is a trouble shooting guide ONLY. Do not run the roaster with the high limit disabled. It is a substantial, safety hazard to do so and Diedrich Manufacturing, Inc. cannot be held responsible if damage occurs as a result. Be sure to reconnect the high limit before using the afterburner.

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