When I am diagnosing a kiln over the phone the “glow test” is one of the most common tests I have the client perform.   It typically doesn’t take much time, is simple to do, and goes a LONG way to helping determine where to look for a problem with a kiln that is acting up.  It can be confusing, however, to perform if you don’t know how to program it; or to interpret if you don’t know what you are looking for.  So in this month’s Tech Tip, I am going to go into detail on how to perform a “glow test” properly, what you are looking for, and what the results typically mean.

Safety First

lgFiring-Safety-Goggles1383608859893-2050688016I should point out that you will need your kiln gloves and eye protection to do this test. You will be opening up your kiln while it is on FULL BLAST, and we don’t want any burns.  You also should NOT perform this test if your kiln threw a big spark, tripped the circuit breaker, or smells like melted plastic.  Those are symptoms of a bigger problem, and I would NEVER recommend powering up a kiln with those symptoms before checking out a few other things first.


When and why should I do the glow test?

WOULD usually do this test if my kiln suddenly would not get to cone AND DID NOT trip a breaker, smell like burned plastic, or throw a big spark.  I would also do the glow test on a kiln if I suspected a single element was broken, and/or threw an FTL or ERR-1, or E–1 error message; to determine which element was the problem (assuming I didn’t have a multimeter, and could not visually find the break.)  Typically, the purpose of the glow test is to help determine if a heating problem is in the control circuit OR in the elements.

How to do it

First:  Empty the kiln – you need to be able to see the element grooves

Second : have your gloves and goggles handy

Third: Close all the peep hole plugs, and close the lid (no need to turn on any vent)

THEN: you are ready to go

Manual kiln with Low-Med-High, Toggle, or INF Switches:



A manual kiln is the easiest kiln to perform the glow test on.  Put ANY cone in the sitter, push in the plunger, and turn the switches straight to HIGH (or ON for toggle).  Now WAIT for about 10-15 min.  Then put on your safety equipment, turn the lights off in the room, and take a peek in the kiln (either ehswitch-oldthrough the peep holes OR by opening up the lid CAREFULLY.  Note which element grooves are glowing.  It helps to number the grooves from the top to bottom.  If any grooves are NOT

kiln-knobsglowing, close the lid and wait another 10 minutes and re-check.  Most (but NOT ALL) elements should be glowing after 20 min on high.  After the re-check, turn the kiln off

Manual kiln with Timer Switches

ACF68CPut ANY cone in the kiln sitter, and push the button in.  Turn the timer switches to either the ON or MANUAL setting on the dial.  Then wait and check as above.  Turn off when done.

Manual kiln with motorized timer switch



Put kiln speed on FAST FIRE, or the highest setting.  Set Kiln Sitter as above, OR if you have a thermocouple shutoff, turn temperature shutoff to 1000 degrees F.  Set any countdown timers to 0 or manual.  Turn thumbwheel to highest numbered setting, and any remaining switches to high.  Wait and check as above.  Turn kiln off when complete

Computer-controlled kiln

31030b v6cf2 faceplate feature-dynatrol-950 RM2A5

You need to input a user-defined program.  The button choice will likely say ‘Enter Prog’, ‘Ramp Hold’, ‘Ramp’, or ‘Step’.  Your kiln’s manual will go over user defined programs in some detail, and will be specific for your kiln.  I would LOVE to put all of the different program styles here keystroke-by-keystroke, but there are simply too many options out there.  I will put the specific variables instead.  Input them into the fields when your controller asks for them:

  • Choose a USER program number that you don’t typically use, so you don’t have to re-type the glow test the next time you need to run it.  I typically store my glow test program as USER 6
  • The program will have 1 segment, or step
  • The Rate of Climb will be 9999 or FULL, depending on controller model
  • The temp for the segment will be 1000 deg F (538 C).  But we won’t let it go that far.  We just need to choose a temperature that is high enough to allow the elements to be on long enough to glow.
  • Any PrHT setting will be set to 00.00
  • The ALAR setting should be set to 9999

Remember to press enter after each setting to accept the changes and move onto the next setting.


Once programmed, make sure the kiln is empty, close the peep holes and lid, then start the program.  Wait and visually check the elements just like a manual kiln.  Stop the program when you are done with the glow test.

What does the glow test tell me

IMG_7225.2IF all the elements glow, then it is likely that any problems you are having hitting cone are likely due to low power or old elements.  Get a multimeter and check the voltage-under-load of the kiln AND the resistance of the elements to determine which.



Ceramic_Oper_Elementglow_W1IF some of the elements glow, but not all of them, then you need to know how your kiln is wired (a wiring diagram will tell you).  If all of the elements in a circuit are dark, then  I would look at the switch, wires, or relay controlling that circuit for the problem.  If only ONE element in that circuit is dark, it is more likely that that element is broken.

IF NONE of the elements glow, but they still get hot, then they are not broken AND there is no problem with the control circuit.  They are likely worn out, or low-powered. Be careful, though.  Some elements in larger kilns won’t glow until a much higher temperature.  At this point, it is best to get out your multimeter and check the elements and incoming voltage.

So as you can see a “glow test” is a truly helpful diagnostic test that anyone can perform without any special tools or equipment.  The results of this test significantly assist us in narrowing down the possible causes for a heating problem.  For more information about how to perform a glow test on your specific kiln, feel free to contact me here at Bracker’s Good Earth Clays.  We are always happy to help.

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