What to do when you see "FAIL"?


  1. FAIL usually just means a thermocouple is broken. It will read FAILTC3 or TC2 or TC1- telling you which thermocouple is out.
  2. When you inspect the thermocouples often, you can see that they can look old, corroded and even cracked at the tip.
  3. If all thermocouples are the same age, or close to it, replace them all.  The kiln will fire best when all the thermocouples are the same age and style.
  4. FAIL actually means that one of the thermocouple circuits is open- or not connected somewhere.
  5. A complete thermocouple circuit is the DynaTrol or other control, the thermocouple wires, and the thermocouple itself.
  6. The thermocouple could be fine and just the wires got pinched in the control box cover. Or the connection between the thermocouple wire and it's wire terminal could be loose. Or it could just be the thermocouple itself, just worn out from old age.  Though it is rare, the electronic controller could also be the problem.


What happens when a thermocouple fails?

  1. The kiln will shut down automatically if all thermocouples burn out.
  2. The kiln continues to fire if only one or two thermocouples burn out.
  3. This protects your firing in the event of failed thermocouples. Of course, if all three thermocouples fail then the control stops firing.


  1. To test if there is a bad thermocouple or thermocouple extension wire circuit, remove the offending thermocouple connection wires from the terminal on the thermocouple and bind the two colored wires (for Type K thermocouples they are red and yellow) together with electrical tape. The control should read room temperature for that thermocouple (typically 130°F because of the thermocouple offsets).
  2. If it does read room temperature, then the thermocouple is probably bad and needs to be replaced. If the control does not read room temperature, then there is either a bad thermocouple extension wire or the control is bad.
  3. If that test does NOT read room temperature then redo the test by putting a small jumper like a paperclip across the thermocouple terminals directly on the DynaTrol board. If the control now reads room temperature then you have a bad thermocouple extension wire or break in the thermocouple extension wire circuit. If it does not read room temperature then the DynaTrol board needs to be replaced.


  1. Sometimes the code CPLt will be displayed.
  2. This code is always displayed after a successful firing to mean “complete”. If it appears after you attempt to restart the kiln after a FAIL message, or at any other time except for the end of the firing to mean “complete”, then it will have a different meaning.
  3. If CPLt appears randomly it means either your thermocouple wires are burning against the kiln case or your thermocouples are so close to failing that they are giving a reading that is so high that the DynaTrol thinks the firing is over.


  1. FAIL with new thermocouples almost always means a poor connection somewhere in the thermocouple circuit.
  2. Usually it is one of the two center screws on the thermocouple connection block (terminal). If you can get half a turn on these two screws you will probably fix the problem.
  3. Be careful to not tighten the two outer screws as much as you tighten the two inner screws. The outer screws tighten down onto very thin thermocouple wires which can be crushed and will break if tightened too much. The inner screws tighten down onto much thicker wires of the thermocouple itself.
  4. Sometimes a thermocouple wire will be loose in the wire terminal. Look for this by wiggling the thermocouple wire while looking at the back end of the wire terminal.
  5. Sometimes there is a broken thermocouple wire somewhere in the length of wire between the thermocouple and the control. Jupiter and DaVinci kilns have long hanging thermocouple wires. Sometimes these can come up against the kiln and overheat.  Look for any sign of overheating on the thermocouple extension wires. If you find tape on the wires the thermocouple extension wires must be replaced. Thermocouple extension wire is inexpensive - if there are any doubts replace it.


  1. You should not mix exposed thermocouples with sheathed thermocouples because their response rates are slightly different.
  2. It is a good idea to keep a spare set of thermocouples on hand.
  3. You can replace just the thermocouple element instead of the whole thermocouple if you want to save money.
  4. A failing thermocouple or thermocouple circuit can also lead to a condition the control display reads 2400 or CPLt when the control starts up.
  5. See this for how to check the thermocouple tip.
  6. See this for information on thermocouple offset.
  7. See this for information on how to know what thermocouples to get for your kiln.