How to Diagnose a Slow Firing Manually Controlled Kiln

March 24, 2025
TROUBLESHOOTING TROUBLESHOOTING Support> Knowledgebase-FAQs How to Diagnose a Slow Firing Manually Controlled Kiln Look for the nameplate data. Plug the amperage and voltage labeled here into Ohm's Law to determine the resistance for the entire kiln. If the nameplate is missing, you can email the factory to try to resolve the model. Additionally, your manual may contain the serial number and nameplate information (check the back cover). Measure the inside dimensions of the kiln, take any available resistance readings, and let us know whether it has Hi-Med-Low switches on infinite-type switches. Describe any other notable features of the kiln. An emailed digital picture can be beneficial. Measure the total resistance of the kiln. Unplug the kiln or turn off the power if you cannot unplug it when measuring resistance in these circuits. Now, turn all switches to high and turn the kiln sitter on. Measure the ohms from the prongs on the main power cord – from the two "hot" blades, not from the ground or neutral. If there is a reading, it should be within 9% of the value calculated using Ohm's Law. The resistance can only be lower than what the nameplate calculations would indicate if the wrong elements were installed in the kiln or the elements are so old that they are worn down to the point of being squashed into each corner around the kiln. Look for overheated connection if low resistance continues for any length of time and replace elements immediately Measure the resistance of each branch circuit. Turn the switches OFF. The switches must be off, or the meter will read all the branch circuits at once. Measure branch circuit resistance with the kiln power OFF from the two flat prongs (not the ground) of the plug-heads of each kiln section. On other kilns, you need to determine the number of elements in each circuit, how the elements in each circuit are connected, and the power wires for each circuit. Take the branch circuit resistance reading at the point where the power wires connect to the element(s). Determine series or parallel. Look to see if the elements are wired in series or parallel with each other. Even in L&L's latest kilns, you would still need to either remove the element box or refer to the kiln's wiring diagram to determine this. Check individual element resistance. Try to obtain a single element's resistance reading by either calculating it if the elements are in parallel or by measuring it with the meter if they are in series. You may need to disconnect wires to isolate as much as possible of each element. Take a voltage reading in each branch circuit at either the element connection to the power wires or at the control box receptacles on later L&Ls. Measure the voltage at the main power supply. If there is a considerable voltage drop from the main power supply to the element connection, it is likely due to corrosion or a connection problem. Badly corroded connections need to be replaced immediately. Both parts of the connection should be replaced simultaneously. Check your plug and receptacle connections, especially the main power cord and receptacle. If the measured resistance is slightly more than 9% over the calculated resistance and this correlates with the problem (slow kiln), you should ideally replace all the elements, or at least those with readings that are too high. If you do not replace them all at once, the kiln may heat unevenly; this is a much less significant problem with kilns that have a zoned design with ungraded elements rather than with kilns that have graded elements. If all of the element resistances are fine but the resistance of the whole kiln is not, the problem must be in a branch circuit. With the kiln on, run a voltage test on the receptacles or at the connections to each element in each branch circuit to identify the faulty one. With the power off, open the control panel and visually inspect the branch circuits. Check branch fuses if the kiln has them. Locate the two wires that initiate the faulty branch circuit from the group originating from L1 and L2 on the main power block. Follow those wires to where they connect to the first component in line, which is likely to be either a fuse block, a relay, or a switch. With the power on and any kiln-sitters or switches set to High (so that the elements will come on if they can), take a voltage reading at the point where these two wires connect to the first component in line. The reading usually should be the same as what it is at the main power block. If this is not the case, one of the wires between the main power block and the first component is faulty and needs to be replaced. If there is voltage there, then take another reading after the first component at the point where the two wires continue onto the next component or to the element connection. If there is voltage after the component, then the component is working. To determine whether the contactor or the switch is bad, first follow the wires from the load side of the switch to the contactor. With the power all on and the switch set to high, take a voltage reading at the point where the two wires from the switch connect to the contactor. If these readings are the same, then the contactor is bad. If no voltage is present, follow the two wires back up to the load side of the switch and measure the voltage there. If the voltage readings are the same, then the contactor is bad. If no voltage is present, follow the two wires back up to the load side of the switch and measure the voltage there. If the voltage reading is the same, then one of the wires is bad. If there is no voltage present at the load side of the switch (power all on, switch on high, and then ensure the voltage is reaching the switch); if it is not, then the switch is faulty. Replace the switch, and if the problem persists, repeat the test. You will most likely need to replace the contactor as well. If there is no voltage after the first component in line and it is neither a relay nor a contactor, then replace it. If it is a fuse holder, replace the fuse. Usually, a faulty fuse indicates a short circuit somewhere in the circuit. Use a continuity tester to test for faulty fuses. Always check the tightness of connections in a questionable circuit. If there is voltage after the first component, proceed along the circuit from the main power block towards the element connections, testing for voltage before and after every component until the problem is isolated. Voltage readings taken from between the elements (and from between resistors in general) give a reading that reflects voltage that is half the supply voltage with two elements in series and either one-third or two-thirds the supply voltage with three elements in series (depending on which side of the middle component of the series the test lead is placed).

Look for the nameplate data. Plug the amperage and voltage labeled here into Ohm's Law to determine the resistance for the entire kiln. If the nameplate is missing, you can email the factory to try to resolve the model. Additionally, your manual may contain the serial number and nameplate information (check the back cover). Measure the inside dimensions of the kiln, take any available resistance readings, and let us know whether it has Hi-Med-Low switches on infinite-type switches. Describe any other notable features of the kiln. An emailed digital picture can be beneficial.
Measure the total resistance of the kiln. Unplug the kiln or turn off the power if you cannot unplug it when measuring resistance in these circuits. Now, turn all switches to high and turn the kiln sitter on. Measure the ohms from the prongs on the main power cord – from the two "hot" blades, not from the ground or neutral. If there is a reading, it should be within 9% of the value calculated using Ohm's Law. The resistance can only be lower than what the nameplate calculations would indicate if the wrong elements were installed in the kiln or the elements are so old that they are worn down to the point of being squashed into each corner around the kiln. Look for overheated connection if low resistance continues for any length of time and replace elements immediately
Measure the resistance of each branch circuit. Turn the switches OFF. The switches must be off, or the meter will read all the branch circuits at once. Measure branch circuit resistance with the kiln power OFF from the two flat prongs (not the ground) of the plug-heads of each kiln section. On other kilns, you need to determine the number of elements in each circuit, how the elements in each circuit are connected, and the power wires for each circuit. Take the branch circuit resistance reading at the point where the power wires connect to the element(s).
Determine series or parallel. Look to see if the elements are wired in series or parallel with each other. Even in L&L's latest kilns, you would still need to either remove the element box or refer to the kiln's wiring diagram to determine this.
Check individual element resistance. Try to obtain a single element's resistance reading by either calculating it if the elements are in parallel or by measuring it with the meter if they are in series. You may need to disconnect wires to isolate as much as possible of each element.
Take a voltage reading in each branch circuit at either the element connection to the power wires or at the control box receptacles on later L&Ls. Measure the voltage at the main power supply. If there is a considerable voltage drop from the main power supply to the element connection, it is likely due to corrosion or a connection problem. Badly corroded connections need to be replaced immediately. Both parts of the connection should be replaced simultaneously. Check your plug and receptacle connections, especially the main power cord and receptacle.
If the measured resistance is slightly more than 9% over the calculated resistance and this correlates with the problem (slow kiln), you should ideally replace all the elements, or at least those with readings that are too high. If you do not replace them all at once, the kiln may heat unevenly; this is a much less significant problem with kilns that have a zoned design with ungraded elements rather than with kilns that have graded elements.
If all of the element resistances are fine but the resistance of the whole kiln is not, the problem must be in a branch circuit.
With the kiln on, run a voltage test on the receptacles or at the connections to each element in each branch circuit to identify the faulty one.
With the power off, open the control panel and visually inspect the branch circuits. Check branch fuses if the kiln has them.
Locate the two wires that initiate the faulty branch circuit from the group originating from L1 and L2 on the main power block.
Follow those wires to where they connect to the first component in line, which is likely to be either a fuse block, a relay, or a switch.
With the power on and any kiln-sitters or switches set to High (so that the elements will come on if they can), take a voltage reading at the point where these two wires connect to the first component in line. The reading usually should be the same as what it is at the main power block. If this is not the case, one of the wires between the main power block and the first component is faulty and needs to be replaced.
If there is voltage there, then take another reading after the first component at the point where the two wires continue onto the next component or to the element connection. If there is voltage after the component, then the component is working.
To determine whether the contactor or the switch is bad, first follow the wires from the load side of the switch to the contactor.
With the power all on and the switch set to high, take a voltage reading at the point where the two wires from the switch connect to the contactor. If these readings are the same, then the contactor is bad.
If no voltage is present, follow the two wires back up to the load side of the switch and measure the voltage there. If the voltage readings are the same, then the contactor is bad.
If no voltage is present, follow the two wires back up to the load side of the switch and measure the voltage there. If the voltage reading is the same, then one of the wires is bad.
If there is no voltage present at the load side of the switch (power all on, switch on high, and then ensure the voltage is reaching the switch); if it is not, then the switch is faulty. Replace the switch, and if the problem persists, repeat the test. You will most likely need to replace the contactor as well.
If there is no voltage after the first component in line and it is neither a relay nor a contactor, then replace it. If it is a fuse holder, replace the fuse. Usually, a faulty fuse indicates a short circuit somewhere in the circuit. Use a continuity tester to test for faulty fuses. Always check the tightness of connections in a questionable circuit.
If there is voltage after the first component, proceed along the circuit from the main power block towards the element connections, testing for voltage before and after every component until the problem is isolated. Voltage readings taken from between the elements (and from between resistors in general) give a reading that reflects voltage that is half the supply voltage with two elements in series and either one-third or two-thirds the supply voltage with three elements in series (depending on which side of the middle component of the series the test lead is placed).

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How to Diagnose a Slow Firing Manually Controlled Kiln