Error code
C-21
Meaning
Oven heating over
Moderate
What to do
Why this happens
Possible causes include a faulty oven sensor, a malfunctioning main PCB, a damaged heater element, or issues with the DLB relay and broil, bake, or convection heater relays being stuck.
SourceSamsung service manual - 30" Freestanding Self-Cleaning Electric Range