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Error code reference

Dacor Oven Error Code U21

Upper/single oven clean over temperature

Dacor codesDacor oven codes

Upper/single oven clean over temperature - cell center temperature goes over 890°F during self-clean.

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The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What U21 means on a Dacor oven

The U21 error code on a Dacor oven indicates that the upper or single oven cavity has exceeded a critical temperature threshold of 890°F during a self-clean cycle. The self-clean process operates at elevated temperatures, typically in the range of 800°F to 900°F, to incinerate food residue inside the cavity. When the cell center temperature sensor detects a reading above 890°F, the control board registers an over-temperature fault condition and triggers the U21 code to prevent potential damage to oven components or a safety hazard.

The primary system involved is the thermal monitoring circuit, which includes the oven temperature sensor (RTD probe), the electronic control board, and the relay or triac responsible for cycling the bake and broil elements during the self-clean operation. If any of these components malfunction, the oven may fail to regulate heat properly, allowing temperatures to climb beyond the acceptable ceiling. A faulty temperature sensor that reads lower than actual cavity temperature can cause the control to continue energizing the heating elements past safe limits, while a welded relay contact can keep elements energized continuously regardless of control signals.

Because the U21 fault represents a thermal safety event rather than a routine operational error, Dacor specifies that the correct first response is to contact a qualified service technician. Attempting to reset the unit and resume a self-clean cycle without diagnosing the root cause carries a risk of repeated overheating. A technician will need to inspect the temperature sensor calibration, verify control board relay behavior, and confirm that the door latch and thermostat interlock systems are functioning correctly before the appliance is returned to service.

Source: manufacturer service documentation.

Common causes of U21

  1. 01

    Faulty oven temperature sensor

    Part replacement

    A temperature sensor that reads lower than the actual cavity temperature will cause the control board to keep heating elements on past safe limits. Testing the sensor's resistance output at known temperatures can confirm whether it is out of calibration or failed.

  2. 02

    Welded or stuck relay on control board

    Part replacement

    A relay on the electronic control board that has welded contacts will continuously supply power to the bake or broil element even when the board signals it to turn off, causing uncontrolled temperature rise. This typically requires replacing the control board.

  3. 03

    Malfunctioning oven control board

    Part replacement

    If the control board is not properly regulating the duty cycle of the heating elements during self-clean, temperatures can escalate beyond the 890°F threshold. Board failure can be intermittent and may not produce other visible symptoms outside of the self-clean cycle.

  4. 04

    Heavy soil or grease load in cavity

    Wiring / connection

    An extremely heavy buildup of grease or food residue can generate significant secondary heat as it combusts during self-clean, contributing to temperature spikes beyond normal operating limits. This is more of a contributing factor than a standalone cause but should be noted when reviewing the conditions before the fault occurred.

  5. 05

    Door latch or thermostat interlock failure

    Part replacement

    The self-clean cycle relies on proper door latch engagement and thermal interlock switches to manage the cleaning process safely. A failed interlock component can disrupt the control system's ability to monitor and regulate oven temperature during the cycle.

See the test procedure for each cause

Frequently asked questions about U21

What does U21 mean on a Dacor oven?
The U21 code means the upper or single oven cavity exceeded 890°F during a self-clean cycle, triggering an over-temperature safety fault. The control board monitors the cell center temperature throughout the self-clean process and shuts things down when that limit is crossed. This code requires a service call rather than a simple user reset. Operating the self-clean feature again before the cause is identified is not recommended.
Can I fix the U21 error myself?
Dacor's guidance for U21 is to contact a qualified service technician, and that recommendation exists for good reason. The fault involves a thermal safety event, and the components that need to be evaluated, including the temperature sensor, control board relays, and interlock switches, require technical testing equipment and experience to diagnose accurately. Attempting DIY repairs without proper diagnosis risks repeated overheating or component damage.
Is my oven safe to use after a U21 error?
After a U21 fault, you should avoid running the self-clean cycle until a technician has inspected and cleared the oven. Normal bake and broil functions may still operate, but the root cause of the over-temperature event has not been resolved and could affect other operating modes depending on which component failed. Treat the oven as potentially unsafe for self-cleaning until it has been serviced.
Will resetting the oven clear the U21 error code?
Cycling power to the oven may clear the displayed U21 code temporarily, but it does not resolve the underlying condition that caused the over-temperature fault. If the temperature sensor, control board, or relay that caused the fault is still defective, the code will return the next time a self-clean cycle is attempted. A reset should not be treated as a fix.
How much does it cost to repair a Dacor oven showing U21?
Repair costs for a U21 fault will vary depending on which component has failed. A temperature sensor replacement is typically a lower-cost repair, often in the range of $100 to $250 including parts and labor. A control board replacement is more expensive, generally ranging from $300 to $600 or more depending on the specific model and labor rates in your area. A technician diagnosis call is usually required first to confirm the failed component before parts are ordered.

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