C-21 on a Samsung range is a temperature sensor failure. The sensor probe that monitors oven cavity temperature is sending a reading the control board considers out of range, so it stops heating rather than let the oven run without accurate temperature feedback.
What Commonly Causes It
- A temperature sensor probe that’s touching the oven wall instead of hanging freely, throwing off its reading
- A sensor that’s failed or drifted out of calibration with age and repeated heat cycles
- A loose or corroded wire connection between the sensor and the control board
- Food debris or grease buildup on the sensor probe affecting its accuracy
What You Can Check
Once the oven has cooled completely, locate the sensor probe — a small metal rod usually near the back wall or top of the oven cavity, separate from the oven light. Confirm it isn’t bent or touching the oven wall or a rack; it should hang with clearance on all sides. Wipe away any visible grease or food buildup on the probe itself with a damp cloth.
Power-cycle the range by turning off power at the breaker for a minute, then restoring it, and try a bake cycle again. If C-21 returns as soon as you start preheating, the sensor is very likely the problem rather than a positioning issue.
When to Call a Technician
Confirming a failed temperature sensor takes a resistance test against the manufacturer’s specification at different temperatures. Our Samsung range repair technicians perform that test and replace the sensor when needed. See our range repair or replace guide for next steps.
This is an independent repair service and is not affiliated with Samsung.
