What do I do if the kiln stalls?

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  • See the Sales FAQs for Frequently Asked Sales and Preorder Questions
  • The Knowledgebase is organized into a series of questions and answers having to do mostly with technical troubleshooting and understanding of kilns.
  • Although we write this for our own kilns many of these articles apply to other makes - although L&L takes no responsibility for that.
  • Many Knowledgebase articles have Actions, PDFs and Videos associated with them.
  • Actions are specific actions for you to take during the troubleshooting or repair process.
  • Each Action may also have Videos and PDFs associated with it and, in addition, specific Cautions.
What do I do if the kiln stalls?
  1. If for some reason the thermocouple wires touch the hot kiln case, they may melt and fail. The result of this is that the kiln can “stall out”, say CPLt prematurely or display any other number of other random error codes. It may refuse to increase in temperature, and the kiln will just run on and on. If it is re-started, it may work fine for a while. What happens is that the millivolt signal in the TC wire goes to ground, or the two wires in the TC wire are “electrically” connected by the stainless steel melting through the insulation and the “temperature” is then taken right there, not in the kiln. However, the signal received can be so foreign to the microprocessor that the kiln will just stall. The specific Thermocouple Lead Harness needs to be replaced.
  2. Thermocouples close to end of their useful life can cause some of these same problems.
  3. Sometimes excessive ambient temperatures (over 125°F) around the control can cause stalling too.
  4. Corroded connection points can also cause stalling.

Additional Actions to Take

  1. Unplug kiln.
  2. Remove or hinge open the control box.
  3. Remove the Thermocouple Lead Wire from the Thermocouple.
  4. Unscrew the Thermocouple from the kiln.
  5. Remove Thermocouple.
  6. Install a new Thermocouple and screw in place.
  7. Replace Thermocouple Lead Wire and tighten. Be sure to get red matched to the MINUS (Negative) sign and the Yellow matched to the PLUS (Positive) sign.

See this video:

  1. Carefully examine thermocouple tip. This is the exposed welded joint at the end of the thermocouple that is not covered up by the ceramic tube.
  2. To do this you will have to remove the thermocouple from its protection tube (if it is a kiln that has one of our protection tubes). You can do this with the kiln disconnected from power.
  3. Look for corrosion - especially if it severe. These thermocouple tips will oxidize and otherwise corrode over time. That is normal. There is some point, however, at which the corrosion affects the ability of the tip to work (thermocouples work by generating a small voltage at the tip caused by two different metals reacting to each other).
  4. Corroded thermocouple tip

  5. Make sure the two wires are securely joined. One of the things that can cause an intermittent problem is a bad weld. If the two wires touch each other (even if they are not welded) they may work temporarily. However, if the weld is not secure then the wires could separate when the kiln heats up and cause an intermittent failure.
  6. If the thermocouple tip looks healthy then test the control board.