I have a Thermador ME302EP/02 (electric) double oven. The upper and lower ovens are not consistently holding temperature.

I placed two thermometers inside the oven next to the oven temperature sensor and recorded temperatures every five minutes (did not open oven doors throughout the tests; did not use fast heat option nor convection, just bake). Throughout the tests, the temperatures indicated by the two thermometers and the oven panel (reading the oven temperature sensor) were generally consistent with each other (generally within 5°). This seems to indicate that the oven temperature sensors are working properly.

Example tests:
Upper oven only: set to 450, oven heats to 450 within 20 minutes and holds 450 for 20 minutes. Thereafter, the temperature steadily drops to 400 over the next 20 minutes. Stopped test.

Upper oven only: set to 450, after 25 minutes oven beeps indicating at set temperature even though panel and thermometers read only 420. Oven continues to heat to 450 over the next 5 minutes, but does not stop heating, steadily heats to 500 over the next 40 minutes and holds 500 for 10 minutes. Thereafter, the temperature steadily drops to 390 over the next 50 minutes. Thereafter, the temperature steadily increases to 465 over the next 60 minutes. Stopped test.

Lower oven only: set to 400, oven heats to 400 within 20 minutes, but does not stop heating, steadily heats to 465 over the next 60 minutes. Stopped test.

Upper and lower ovens: set both to 400, within 15 minutes upper oven beeps indicating at set temperature even though panel and thermometers read only 380, and thereafter increases to 400. Within 25 minutes from the start, lower reaches 400/beeps, but does not stop heating, steadily heats to 430 over the next 25 minutes. Stopped the test.

Visual inspection of the control module and relay board do not reveal any poor connections nor signs of failure.

I previously replaced the bake elements, despite the prior bake elements not showing any visible signs of failure and passing the multimeter test.

Power is not suspect, newer construction, no signs of issues with breakers, wiring, outlet, etc.

The Thermador service manual indicates that 75% of returned “defective” controls modules were actually not faulty. Would like to avoid cost of replacing if not really the issue.

Wondering whether the symptoms from the tests strongly indicate an issue with the control module, relay board, or something else?

Thanks in advance.