Kiln Relay Q&A - For Kiln Buyers and Owners

Kiln Relay Q&A - For Kiln Buyers and Owners

Kilns, ovens, and furnaces are essential equipment for those who work in industries requiring high-temperature processing. These tools of the trade are used by metallurgists, engineers, lab professionals, potters, glass workers, and others who work with materials that must be fired at either high temperatures, or held at a series of lower temps. Kilns can be complex machines, requiring many components, and the kiln relay in the controller box is one of the most important parts. The quality of the components in a kiln's controller box can make all the difference in the quality of a user's final product.

This article will answer some frequently asked questions about kiln relays, including what they are, how they function, and what to look for when purchasing or maintaining a kiln.

1.  What is a kiln relay?

All relays utilize an electromagnetic field to regulate a switch, according to the technical definition. When a voltage is applied to the coil, an electromagnetic field is produced that attracts the armature to the contact, completing the circuit. The method of switching is determined by the form of relay employed. A kiln relay is an electrical component that regulates the passage of electricity to the heating elements. It functions as a switch that activates and deactivates the kiln's heating elements as required tomaintain the desired temperature. Kiln relays are a vital component of the kiln's electrical system; without them, the kiln would not operate correctly.

2. How does a kiln relay work?

When the kiln is activated, the relay sends an electrical signal to the heating elements, instructing them to begin heating. Once the kiln reaches the desired temperature, the relay turns off the electrical signal that turns off the elements until the temperature falls below a predetermined threshold, at which point the cycle is repeated. The kiln relay is connected to a thermostat (thermocouple) that monitors the temperature inside the kiln and sends signals to the relay to activate or deactivate the elements as necessary.

3. What are the various kinds of kiln relays?

Electromechanical Relays are the most prevalent form of relay. They are made up of an armature, a coil, and a contact. When voltage is applied to the coil, a magnetic field is created that physically draws the metal armature towards the contact, closing the circuit. Mechanical relays, typically encapsulated in plastic, are more economical and less expensive than mercury and solid-state relays, but also less reliable.

Mercury Displacement Relays (MDRs/Reed) are similar to electromechanical relays, but operate using a magnetic field. When a magnetic field is applied to the hermetic glass tube, the two metal contacts close. The liquid metal moves up and down to complete the contacts in the tube; it is the only moving component. Mercury relays are dependable, but they are prohibited in several states due to the mercury's carcinogenic and difficult to dispose of properties.


Solid-State Relays are semiconductor devices that utilize an optical or magnetic coupling to transfer a circuit. They are more reliable and efficient than electromechanical relays due to their lack of moving elements. Solid-state relays are more durable than mechanical relays and mercury relays, making them the preferred relay.



      4.  What should I look for when purchasing a kiln? (Why should I care about relays?)

      It is essential to purchase a kiln with a dependable and high-quality relay. If a relay is the  regulator of electric current in your kiln and if fails in the open position, no current will flow and there will be no electricity to the coil and thus, no heat.  If the relay fails in the closed position, the current will continue to flow unchecked and the coil will get too much heat causing an over fire!  No heat is uneventful, because nothing will happen, but too much heat can be a kiln killer.  The over fire could result with a mess in unconfined glass flow, melted or flattened clay, ruined brittle metals, or even end up with a fire situation if left unattended. Larger kilns with multiple relays may be a bit more forgiving, because one of failed relay but you will not achieve an accurate firing and you will suffer an unsuccessful heat treatment. Consider upgrading to a kiln with a solid-state relay, as these are more dependable and durable than mechanical or mercury relays. (See the end of the article for a list of benefits.)

      5. How long do kiln relays last, and when should they be replaced?

      There isn’t a solid answer to this question.  If you have mercury or solid-state relays, they could very well last the life of your kiln.  A periodic visual inspection of the relays is usually all that is necessary. Depending on variables such as usage frequency, maintenance, and environmental conditions, the lifespan of a kiln relay can vary.

      Mechanical Relays have a shorter lifespan, with a well-maintained relay lasting several years and an improperly maintained or overused relay failing sooner. Mercury and solid-state relays have a projected lifespan of up to 15 to 20 years. Mechanical relays are projected to last 18 to 36 months.  knowing this, mechanical relays fail because of use and wear.  If you are firing your kiln, oven, or furnace unit once a month, your mechanical relays will last much longer than if you are firing it two or three times a week.  It is best to replace your relays every 18-24 months to be on the safe side.

      6. How do I know if my kiln relay requires replacement?

      If the kiln is not properly heating up, or if the temperature is fluctuating more than usual, it may be a sign that the relay is malfunctioning. In addition, you may observe that the relay is buzzing or producing a louder-than-usual clicking sound, or that the contacts are discolored, pitted, or corroded.

      7. How do I determine if the relay failed?

      There are several indicators of a malfunctioning kiln relay, including:

      1) Overheating: If a kiln relay is trapped in the closed position, the kiln may overheat and suffer damage to itself and/or its parts.

      2) Burning odor: If the kiln emits a burning odor, the relay may be malfunctioning or overheating.

      3) Kiln not heating: If the element is not heating at all, despite having programmed the kiln to commence, a faulty relay may be the cause.

      8. What are some typical issues with kiln relays?

      Common issues with kiln relays include contact erosion and corrosion on mechanical relays, connection loss or damage, and overheating. These problems can result in a loss of temperature control and injury to the kiln and its components.

      9. How do I preserve my kiln relay?

      Regular maintenance can extend the life of a kiln relay with proper care. Regularly inspect the contacts of a kiln with mechanical relays for signs of wear or corrosion, clean this up when necessary. You can clean the contacts with a delicate cloth or fine sandpaper, taking care not to damage them. Inspect the wires and connections for signs of damage or deterioration, and if necessary, replace them. Check for heat damage on a relay. It will look like a melted spot in the plastic body. It is likely that a push-on terminal of a wire connected to the relay near that burned spot will be loose. This is because excessive heat reduces the spring tension of the terminal. If this is the case, replace the push-on terminal on the wire before installing a new relay. Otherwise, the loose terminal will destroy the new relay. This is because a loose connection produces tremendous heat. This is unnecessary for kilns equipped with mercury or solid-state relays, as these typically do not require maintenance.

      10. Can I replace the relay on my own?

      Replacement of a kiln relay can be a challenging endeavor; if you lack experience with electrical devices, it is advised that you seek the assistance of an electrician or kiln technician. However, if you or a friend are familiar with working with electrical components and are confident in your abilities, you are probably able to replace the relay on your own. Carefully adhere to all safety guidelines and manufacturer instructions.

      11. How much does it cost to replace a kiln relay?

      The cost of replacing a kiln relay can vary based on the type, brand, and labor cost of the relay. Depending on the complexity of the task, the cost of labor can range from $50 to $200 or more.

      12. Where can I purchase a new kiln relay?

      You can purchase a replacement kiln relay from kiln manufacturers, your kiln distributor, online retailers, and local kiln supply stores. Ensure that the relay you purchase is compatible with the model and specifications of your kiln. Have the model and serial number of your kiln available when placing an order.

      14. Can I upgrade my kiln relay?

      Yes, you can upgrade your kiln relay to a newer, more dependable type. However, this may necessitate expensive new wiring in your controller unit. Consult with a kiln technician or electrician to determine the ideal relay for your kiln and to ensure that the upgrade is performed correctly and safely.

      14. What should I do if my kiln relay stops working?

       If your kiln relay fails, you must promptly unplug and turn off the kiln. Do not attempt to use the oven until a qualified technician has replaced or repaired the relay.

      15. How can I avoid kiln relay failures?

      A variety of conditions, including voltage spikes, power surges, and power disruptions, can damage a kiln relay. In addition, the relay can malfunction if it is exposed to excessive heat or moisture. It is essential to safeguard your kiln and its components by installing whole-house or shop surge protection and maintaining a cool, dry environment for the kiln. Never use a plug-in surge protector on an extension cord in conjunction with a kiln. Regular maintenance and correct utilization of the kiln can prevent relay failures. Regularly clear the contacts and connections, avoid overloading the kiln, and adhere to the manufacturer's care instructions.

      Kiln Relay FAQs

      Can I use a mechanical relay in my kiln instead of a solid-state relay?

      Although mechanical relays are less expensive than solid-state relays, they are less reliable and have a limited lifespan. For optimal dependability and durability, it is advised that you use a solid-state relay in your kiln.

      How frequently should I clean the kiln relay's contacts?

      It is recommended that you clean the contacts on your kiln relay at least once a year, or more often if you use your kiln frequently or if you work in a dusty or unclean environment.

      Can a faulty kiln relay damage my kiln?

      Yes, a malfunctioning kiln relay can damage your kiln and its components by allowing the temperature to vacillate uncontrollably or by causing the kiln to overheat.

      How can I tell if my kiln relay is malfunctioning?

      Indicators of a faulty kiln relay include erratic temperature control, inability to reach the desired temperature, and a smoldering odor emanating from the kiln.

      Can I test my kiln relay to determine if it is functioning correctly?

      Yes, you can use a multimeter or other electrical diagnostic equipment to test the kiln relay. If you are unfamiliar with electrical testing procedures, however, it is recommended that you seek assistance from a qualified technician.

      A Note on the Advantages of Solid-State Relays

      Solid-state relays have several advantages over their electromechanical and mercury-displacement counterparts. They are more dependable, efficient, and quiet, and they offer precise temperature and electricity control.

      Solid-state relays have greater reliability and durability than other relay varieties. Due to the absence of moving parts, mechanical wear and strain cannot occur.

      Solid-state relays can transform on and off considerably more quickly than electromechanical relays. This means they have precise control over the temperature and electricity of the kiln.

      Solid-state relays are more energy-efficient than alternative relay varieties. They do not generate heat and require less energy to turn on and off.

      Solid-state relays produce less noise than electromechanical relays. They do not emit annoying noises such as clicking or buzzing, which can be distracting in a workshop.

      Solid-state relays are safer than mercury-displacement relays because they do not contain any hazardous substances.

      Need to order replacement relays? This form can help!
      Or if you know what you need, here is a link to order mechanical relays (Make sure you have the Kiln Manufacturer, Kiln Model Name, Kiln Serial Number Ready to Order) Click Here.

      As always, feel free to reach out to our experienced team with questions or comments. We're always here to help! Give our technical team a call at (210) 446-9979 or email us at