Legacy Thermador CM/CJ Lower Oven Showing F21: Lower CANCEL Key Shorted High

What F21 means

A lower-oven F21 on a Thermador C, CM or CJ model from the older C271 through CJ302 group means the lower CANCEL key reads as shorted high. This is the lower twin of the upper-oven code, and the legacy service table gives it the same checks. Newer Thermador ovens can use F21 for a different problem, so the model number decides how we read it.

Usual causes of F21

Wiring between the control display board and the touch panel
Worn display board, touch panel, or both

✓ A safe check worth trying

1. Clean the panel gently with a dry cloth and check nothing is resting against it. 2. Turn the oven's power off at the breaker for three minutes. 3. Turn it back on and read the display. 4. If F21 shows again, call us with the code. Do not pull the panel loose yourself.

! Why you should stop here

A clean-looking display can hide a ribbon problem that only a visual check finds
Panel parts are sold as an assembly or separately depending on the model
Quotes come in writing first, with parts confirmed by model number

Taking off a panel yourself does not by default void a manufacturer warranty, yet it can lead to accidental damage, and some manufacturers attach their own service terms. Read your warranty paperwork, or ask us, before you decide.

→Same appliance

More Oven codes

E15Thermador Legacy Oven, Dreefs Control Code E15: Board Replacement on CT/CMT Models F34Thermador Legacy C/CM/CJ Oven F34: Upper Oven Cooling Fan Air Switch Not Detected F83Reading F83 on Older Thermador C/CM Wall Ovens (Lower Door Stuck Position) ErrThermador POD Built-In Oven Err on Legacy POD301, POD302, PODC302, PODM301 and PODMW301: Invalid Temperature F10Thermador C-Series Wall Oven F10 on C/CM/CJ Models: Power Board Incompatibility F40Thermador Oven F40 on Older C-Series Models: Upper Meat Probe Shorted F84Thermador Wall Oven F84 on Legacy C/CM-Series Ovens: Lower Latch Input Shorted E + numberThermador POD301 and POD302 Oven E + number: Display Code With Beeping

F21F21 questions

Is F21 the lower oven version of F20?

Yes. The source lists F20 for the upper oven CANCEL key and F21 for the lower one, with F21 using the same checks as F20.

Do I need a whole new control for F21?

Not necessarily. The source lists the display board, the touch panel, or both. We test the connections first and quote only what the evidence supports.

Can I use the upper oven with F21?

The code names the lower oven's key, so the upper cavity may work normally. Because both share the control, we suggest a full check on the visit.