Thermador Oven Error Code F21

The F21 code on a Thermador oven means the lower oven cancel key has been detected in a shorted high condition. The control board is reading the cancel key as continuously active rather than responding to a momentary press. This points to a fault in the keypad membrane, ribbon cable, or in some cases the control board itself.

It is generally not recommended to continue using the oven while this fault is active. A shorted cancel key input can cause unpredictable control behavior and may interfere with the oven's ability to stop operation correctly. Discontinuing use until the fault is diagnosed and repaired is the safer course of action.

Resetting the oven by cutting power at the breaker for a few minutes may temporarily clear the F21 code, but it will return if the underlying fault in the keypad or wiring has not been corrected. A reset is useful for confirming whether the fault is intermittent or persistent, but it is not a repair. The root cause must be identified and corrected to permanently resolve the error.

Some causes of the F21 code are approachable for a knowledgeable DIYer. Cleaning moisture or contamination from the keypad surface and reseating the ribbon cable connector are low-risk steps. However, replacing the keypad membrane or control board requires disassembly of the control panel and working near electrical components, so comfort with appliance repair is important before proceeding.

Repair costs depend on which component has failed. A replacement keypad membrane typically falls in the range of $50 to $150 for the part, while a control board replacement can range from $150 to $400 or more for the part alone. Adding professional labor, total repair costs can range from $150 to $600 depending on the diagnosis and parts needed.