Kenmore Oven Error Code F21

F21 on a Kenmore oven means the User Interface Board has lost communication with the Appliance Control Board. The UIB is no longer detecting any incoming signals from the ACB, which prevents normal oven operation. This is an electronic control communication fault, not a heating or sensor error. The cause can range from a loose wire harness to a failed control board.

It is not recommended to use the oven while F21 is active. The communication failure between the two control boards means the oven cannot properly coordinate its functions, which could result in unpredictable behavior. The oven should be diagnosed and repaired before being returned to regular use.

Repair costs depend on which component is at fault. If the fix is a reseated or replaced wiring harness, costs are relatively low, generally in the range of $50 to $150 for parts and labor. Replacing an Appliance Control Board or User Interface Board typically runs between $150 and $400 or more, depending on parts pricing and local labor rates. Getting a professional diagnosis first can help avoid replacing the wrong component.

Some causes of F21 are DIY-friendly, particularly if the problem is a loose or disconnected wiring harness connector. Start by checking the harness at connector P20 on the Appliance Control Board and connector J2 on the User Interface Board. If the wiring looks intact and secure, diagnosing a failed board typically requires more advanced electrical knowledge and may be better left to a qualified technician.

Resetting the oven by cutting power at the breaker for a few minutes may temporarily clear the F21 code, but if the underlying cause is a wiring or board problem, the error will return. A reset is a reasonable first step to check whether the fault is intermittent, but a persistent F21 code requires physical inspection of the communication harness and control boards.