Why does my kiln seem like it overfires the pottery?

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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.
Why does my kiln seem like it overfires the pottery?

The work is overfired but there is no error code. Here are some things to look for:

  1. Cones placed wrongly in cone pack- angle is off
  2. Small or wrong cones used
  3. Fired to the wrong cone
  4. Firing with a hold time at the end
  5. Firing a Vary Fire program to too high a temp for the rate of climb
  6. TC offset adjustment needs to be set higher
  7. TCs reading unevenly (from age or loading unevenly or too close to TC) make it take longer to even out(must be firing and hot to see this; press 1,2,3),
  8. Old elements have more and more trouble responding to uneven temps- (from TC age or from uneven loading or loading too close to the TC) this makes the kiln take longer and can make cones look like an overfire
  9. Kiln-sitter (if used) out of adjustment
  10. Kiln-sitter (if used) blobs the cone instead of bends it- replace kiln-sitter tube
  11. Lid/ Hinge out of adjustment- opens a bit in the front when hot.

Additional Actions to Take

Checking Elements

EASY-FIRE, DURA-FIRE, EQUAD-PRO, LIBERTY-BELLE

  1. With all power OFF, pace the test leads of the multimeter of the each of two of the terminals marked 1 and 2, 3 and 4, or 5 and 6 on the element terminal strip. Compare the reading you get to the reading you get from the other element terminals. Also check against the wiring diagram for the ohms listing.

JUPITER, DAVINCI

  1. With all power OFF, pace the test leads of the multimeter of the two flat prongs of each section's jumper cord, one on each prong, OR on both connecting wires, at the connection points with the elements. Compare the reading you get to the reading you get from the other jumper cords or connecting wires. Also check against the wiring diagram for the ohms.

See this tutorial on how to use a multimeter.

Ensure Kiln Has Been Programmed Correctly
  1. Make sure you have programmed the kiln properly and it is supposed to be firing.
  2. Read the Operation instructions.
Fix Lid Seal

Fix lid seal if a bright red glow is visible around the seal when kiln is operating and/or excessive heat loss can be felt around seal.

  1. Rub seal high points down with sandpaper until no more than 1/16 of an inch gap is found at any point along seal.
  2. Check for unevenness in the gap that will cause an excessive heat loss.
  3. Replace lid if it is excessively cracked or worn or has holes in it. Replace lid.
Place Cone Packs Kiln

Use cone packs in all sections (top, center, bottom) of the kiln and keep records of what happens.

Replacing Elements
  1. Unplug kiln.
  2. Remove the Control Box.
  3. Using a 3/8" nut driver or ratchet wrench or adjustable wrench, remove the nuts that hold the element end onto the Element Terminal Bolt. Note that the terminal bolt head is held in place by an inset shape on the underside of the ceramic terminal block and it will not turn much.
  4. Untwist the element end from around the Element Terminal Bolt. Straighten it out as much as possible.
  5. In most cases the element can be lifted out of the holder at this point. Sometimes, if the element has really disintegrated, you need to remove it in pieces with needle nose pliers.
  6. If element is hard to get out of the holders (because of growth of the element) you can try heating up the kiln slightly so as to heat up the element slightly to just the point where element is slightly pliable–don't let it get red. This will soften the wire. Then turn off the kiln and disconnect all power to the kiln. Using heat protecting gloves and a pair of needle nose pliers pull out the softened element.
  7. From the inside of the kiln, using needle nose pliers, grab the element as close to where it goes through the brick wall to Terminal Block. Pull the element end through the hole. Be careful not to enlarge the hole in firebrick. The brick is soft and will not take much abrasion.
  8. Be sure to check for failure points for evidence of contamination on the element and the element holder. If the element holder is contaminated it will cause rapid failure of the new element. Replace contaminated holders with the new ones.
  9. Using your multimeter check the resistance of the new element.
  10. Install the twisted ends of the elements through the holes in the wall of the kiln. Element ends should be straight at this point.
  11. Pull them up tight up to the wall of the kiln by pulling from outside the kiln.
  12. Lay the element into the groove. Note that the unfired element is going to have some springiness to it before it is fired for the first time. You may need to use a screwdriver to press the element into the holder. YOU DO NOT NEED PINS.
  13. FOR KILNS WITH NON-CERAMIC TERMINAL BLOCK OR ON RETROFITTED KILNS WHERE YOU HAVE ADDED A CERAMIC TERMINAL BLOCK BUT STILL NEED BUSHINGS: Be sure to replace the insulators and spacers over the element tails.
  14. Consulting your picture or labeling, wrap the appropriate element tails around the appropriate element connection bolt, clockwise, one around and cut off the excess tail.
  15. Install the elements and hardware: Place the wires from the jumper cord or connecting wires onto the appropriate bolts and tighten with stainless steel nuts.
  16. A washer goes under the first element.
  17. Twist the first element end CLOCKWISE around the Terminal Bolt.
  18. The next element gets twisted around the Terminal Bolt on top of the first element.
  19. Another washer goes over the Terminal Bolt.
  20. Place a nut on top and tighten it.
  21. Put another washer on.
  22. Put on the Ring Terminal of the Power Lead Wire.
  23. Put another washer on.
  24. Put another nut on and tighten it. How much the nut can be tightened is dependent on how tight the element connection bolt is on the element connection board. A tight connection is very important, but if you tighten too much and twist the element on the bolt too far you could break the element, the bolt, or the insulator.
  25. Reattach the ground wires and the element box if the kiln has them. DO NOT FORGET TO ATTACH GROUND WIRES. IF EACH KILN SECTION IS NOT GROUNDED THIS CAN BE VERY DANGEROUS.
  26. Test the resistance at the jumper cord's plug head or at the other end of the connecting wires.
  27. Reattach the control box, turn on the kiln and make sure all the elements come on.

See this tutorial on how to use a multimeter.

See this video:

Replacing Thermocouples
  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 Plus sign and the Yellow matched to the minus sign.

See this video:

Applies to these Kiln Series

Applies to these Old Kiln Series