Every potter who fires their own kiln eventually runs into problems — a firing that doesn’t reach temperature, glazes that look wrong, pieces that crack, or a kiln that behaves differently than expected. Most kiln problems have straightforward causes and fixes once you know what to look for. Here is a guide to the most common issues and how to resolve them.
Kiln Not Reaching Temperature
Symptoms: Controller shows target temperature reached but witness cones are underbent. Kiln takes much longer than usual to fire.
- Aging or failed elements — the most common cause. Elements lose efficiency over time. Check with a multimeter — increased resistance compared to baseline readings indicates aging elements. Replace if significantly degraded.
- Drifting thermocouple — a thermocouple that reads low will cause the controller to shut off before the kiln actually reaches temperature. Verify with witness cones and replace the thermocouple if needed.
- Overloaded kiln — too much mass in the kiln slows heating. Reduce load size or extend firing time.
- Electrical issues — check that the kiln is receiving full voltage. A tripped breaker or loose connection can reduce power output.
Uneven Firing — Hot and Cold Spots
Symptoms: Witness cone packs on different shelves show different results. Glazes look different on top versus bottom of kiln.
- Uneven element wear — elements in different sections of the kiln age at different rates. If one section fires cooler than others, those elements may need replacement.
- Poor loading — shelves that fit too snugly block heat circulation. Leave space between shelves and kiln walls.
- Blocked thermocouple — if the thermocouple is positioned near a cold spot, the controller cuts off too early for the rest of the kiln. Check thermocouple placement in your kiln manual.
- Fix: Use witness cones on multiple shelves to map your kiln’s hot and cold spots, then adjust loading to compensate — heavier pieces in cooler zones, lighter pieces in hotter zones.
Pieces Cracking During Firing
Symptoms: Pieces crack or shatter in the kiln, often with a loud pop.
- Pieces not fully dry — the most common cause of cracking. Any residual moisture in the clay turns to steam during firing and can crack or shatter pieces. Always ensure work is bone dry before loading.
- Firing too fast — ramping up too quickly in the early stages (below 250°F) traps steam. Slow the initial ramp to 80–100°F per hour.
- Cooling too fast through quartz inversion — rapid cooling around 1063°F (573°C) can crack even well-fired pieces. Let the kiln cool naturally and do not open before 200°F.
- Glaze fit issues — glazes that shrink or expand significantly differently from the clay body can cause delayed cracking after firing. See our guide on glaze crazing.
Glaze Fused to Kiln Shelf
Symptoms: Piece is stuck to the shelf after firing.
- Glaze on the base of the piece — always wipe the bottom quarter inch of every glazed piece before loading.
- Insufficient kiln wash — reapply kiln wash to bare spots on shelves before every firing.
- Fix: Tap the piece gently with a mallet to break the bond. If it won’t release, use a chisel carefully at the glaze line. Grind the shelf smooth and reapply kiln wash before the next firing.
Element Failure
Symptoms: Kiln fires unevenly, takes much longer than usual, or fails to reach temperature. Visible break or sag in an element coil.
- Elements have a limited lifespan — typically 100–200 firings for mid-fire work.
- Always replace all elements at the same time — mixing old and new creates uneven firing.
- Order replacement elements from your kiln manufacturer with your kiln model number — element specifications vary between kilns.
Kiln Firing Error Codes
Modern digital controllers display error codes when something goes wrong. Common ones include:
- FAIL or E- codes — usually indicate the kiln is not heating fast enough, often caused by element failure or a thermocouple problem
- tC errors — thermocouple errors. Check that the thermocouple is properly connected and not damaged
- Consult your controller manual for the specific codes for your model — Skutt, L&L, and Paragon all use slightly different codes
For more on firing, see Kiln Firing Guide. For maintenance, see Electric Kiln Maintenance Guide.
