How to Check Your Kilns Relay
Is your kiln not reaching temperature? Maybe it shuts off halfway through a firing? Before you call in for repair, it’s worth taking a look at one small but essential part: the relay.
Relays manage the electrical flow to your kiln's heating elements. If they fail, your work could underfire, crack, or even suffer complete loss. A quick relay check every 6-12 months can prevent these issues, protect your studio, and help you fire with confidence.
Let's walk through how you can inspect this critical component and keep your kiln running strong.
Understanding Kiln Relays
What Is a Kiln Relay?
A kiln relay controls when your heating elements turn on and off based on the temperature you set. Without relays, your kiln couldn’t regulate its heat properly. They work by opening and closing to manage the powerful 240-volt current that fuels your firings.
To better understand how kilns compare to other heating devices, check out our full overview of kilns, ovens, and furnaces.
There are three common types of kiln relays:
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Mechanical relays: These use metal contacts to open and close circuits.
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Mercury relays: These contain liquid metal that shifts to complete a connection.
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Solid-state relays: These use electronic components instead of moving parts, making them quieter and longer-lasting.
Common Relay Failure Modes
Relays usually fail in one of two ways: stuck open or stuck closed.
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Stuck open: Electricity can't reach your heating elements, causing cool spots or making it impossible to hit your target temperature. Your pottery may come out underfired or inconsistent.
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Stuck closed: Power keeps flowing even when it shouldn’t. This can push your kiln past safe temperatures, risking damage to your kiln, your pieces, and even your studio.
Either way, regular inspections are your best defense against surprise problems.
Signs of Relay Issues
Here are some signs that your kiln relay might have some issues you need to address.
Observable Symptoms
Relay issues often show themselves before an entire firing fails. Keep an eye (and ear) out for:
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Uneven heating across the kiln
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Temperature readings more than 50°F off from your program
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Darker areas inside the kiln
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Missing the usual clicking sounds when the kiln heats up
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Electrical buzzing (around 60Hz)
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Error codes on your digital controller
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Firing cycles taking much longer than normal
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Kiln stopping suddenly mid-firing
If you notice any of these warning signs, checking your relays should be your first step.
It’s also smart to test your kiln’s thermocouple to make sure temperature-sensing issues aren’t the root cause.
How to Check Your Kiln’s Relay
Check your kiln’s relay with these step-by-step instructions. Safety is first, so make sure to follow our precautions below:
Safety Precautions
Always:
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Unplug your kiln or shut off the breaker.
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Allow the kiln to fully cool. Larger kilns may need several hours.
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Wear heat-resistant leather gloves and ANSI-approved safety glasses.
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Confirm surface temperatures are under 120°F before starting.
Kilns operate at dangerous voltages. Never rush this step.
Visual Inspection
Once it's safe:
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Open your kiln’s control panel to locate the relays.
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Look for signs of trouble like:
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Burn marks or charred spots
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Melted plastic parts
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Discolored connection points (yellow or brown)
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Blackened relay contacts
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Cracked or brittle wire insulation near connections
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A burnt or acrid smell
All wire connections should be tight. Gently test them and use a 1000V-rated insulated screwdriver if any need tightening.
Functional Testing
You can take it a step further with a digital multimeter:
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Set the multimeter to resistance (Ω) or continuity mode.
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With the kiln still disconnected, place the probes on the relay’s load terminals (usually labeled L1/L2 or T1/T2).
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A working relay will show infinite resistance (open circuit) or clear continuity when activated.
For a basic test:
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Program your kiln to heat to a low setting (around 300°F).
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Let it stabilize, then power it off and inspect the heating elements.
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Uneven element heating can point to relay problems.
Uneven element heating can point to relay problems.
If you’re seeing additional issues during testing, our kiln troubleshooting guide can help you diagnose and fix common problems quickly. Exercise extreme caution. Internal components can stay dangerously hot.
Preventative Maintenance Tips
Regular Inspection Schedule
Make relay checks part of your routine maintenance:
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Hobbyists: Inspect once a year.
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Heavy users: Inspect every 3-4 months, especially if firing at high temperatures.
Keep a maintenance log. Track:
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Inspection dates
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Observations
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Any replacements (include model and serial numbers)
It helps spot patterns and makes service calls smoother if you ever need extra help.
Upgrading Relays
Thinking about upgrades? Solid-state relays offer major benefits:
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No moving parts to wear out
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Silent operation
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Extremely long lifespan (up to 100,000 firing hours)
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Consistent temperature control
When you're ready to put your kiln to better use with upgraded parts, our guide can walk you through the best options for your setup.
While they cost more upfront ($85-$150 compared to $40-$60 for mechanical relays), they pay for themselves in reliability and fewer ruined firings.
If your kiln uses mercury relays (the ones with silver liquid inside glass tubes), you should know that many areas are phasing them out due to environmental concerns. Always dispose of mercury components properly through a certified hazardous waste facility. Some manufacturers even offer trade-in discounts when you switch to solid-state options.
Related: Can You Use a Kiln at Home? How to Use
Small Steps Today, Big Savings Tomorrow
By learning to check your kiln’s relay, you're taking an important step toward protecting your studio, your equipment, and your creative work. Simple inspections a few times a year can prevent expensive repairs and avoidable firing failures.
Remember:
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Set regular inspection dates based on how often you fire.
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Always prioritize safety.
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When in doubt, reach out to a certified technician.
A little attention today keeps your kiln firing happily for years to come, and gives you more time to focus on creating the pieces you love.
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