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Error code reference

Dacor Oven Error Code U43

Upper/single relay board no zero crossing (ZC) detected on relay board.

Dacor codesDacor oven codes

Upper/single relay board no zero crossing (ZC) detected on relay board.

First step from the service manual

Verify connections are proper on S19 (double line break relay). Secure connections at S19, then replace relay board.

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

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What U43 means on a Dacor oven

The U43 error code on a Dacor oven indicates that the upper or single relay board is not detecting a zero crossing (ZC) signal. Zero crossing detection is a fundamental function of the relay board that monitors the AC power waveform. The relay board uses this signal to synchronize relay switching with the natural zero voltage points of the AC sine wave, which protects relay contacts from arc damage and ensures proper timing for heating element control. When the ZC signal is absent, the board cannot operate the relays safely or correctly, and the oven halts normal operation.

The most common entry point for diagnosis is the S19 connector, which is the double line break relay connection on the relay board. Loose, corroded, or improperly seated connections at S19 can interrupt the signal path between the relay board and the AC line input, causing the board to report no zero crossing activity. Because zero crossing detection depends on a clean, stable line voltage reference, any break or high-resistance connection in that signal path will trigger U43.

If securing and verifying the S19 connections does not resolve the fault, the relay board itself is likely defective. Internal component failures on the relay board, such as a failed zero crossing detection circuit, damaged optocoupler, or degraded signal conditioning components, will prevent the ZC signal from being generated or recognized regardless of external connection quality. In that case, replacing the relay board is the required repair.

Source: manufacturer service documentation.

Common causes of U43

  1. 01

    Loose or unseated S19 connector

    Wiring / connection

    The S19 double line break relay connector may be loose, partially disconnected, or improperly seated on the relay board. This interrupts the zero crossing signal path and is the first thing to check before replacing any parts.

  2. 02

    Corroded or damaged S19 connector pins

    Part replacement

    Corrosion or physical damage to the pins or terminals at the S19 connector can create high resistance in the signal path, preventing a clean zero crossing signal from reaching the relay board detection circuit.

  3. 03

    Failed upper or single relay board

    Part replacement

    If the S19 connections are secure and in good condition, the relay board itself may have a failed internal zero crossing detection circuit. This is a common outcome when connector checks do not resolve the U43 code, and board replacement is required.

  4. 04

    Wiring harness damage between relay board and line input

    Part replacement

    Damaged, pinched, or broken wiring in the harness leading to the relay board can sever the signal path needed for zero crossing detection. Inspect the harness for signs of heat damage, abrasion, or breaks.

See the test procedure for each cause

Frequently asked questions about U43

What does U43 mean on a Dacor oven?
U43 means the upper or single relay board is not detecting a zero crossing signal from the AC power line. Zero crossing detection is required for the relay board to safely time and control the oven's heating elements. The oven will not operate normally until this signal is restored. The fault is typically caused by a loose connection at the S19 connector or a failed relay board.
Can I fix the U43 error myself?
The first diagnostic step, checking and securing the S19 connector, is something a confident DIYer can attempt after unplugging the oven and allowing it to cool completely. However, if that does not resolve the code, replacing the relay board involves working inside the oven's electrical cabinet, which carries serious shock hazards. At that stage, a qualified appliance technician is strongly recommended.
Is it safe to use my Dacor oven when U43 is displayed?
No, you should not attempt to use the oven while U43 is active. The error indicates the relay board cannot properly control the heating elements, which means the oven may not heat correctly or may not shut off as intended. Discontinue use until the fault is diagnosed and repaired.
Will resetting the oven clear the U43 error code?
A power reset, such as turning off the circuit breaker for a minute and restoring power, may temporarily clear the displayed code, but it will not fix the underlying problem. If the S19 connection is loose or the relay board is defective, the U43 error will return once the oven attempts to operate again. A reset is not a substitute for proper diagnosis and repair.
How much does it cost to repair a Dacor oven with a U43 error?
If the repair only requires reseating the S19 connector, the cost may be limited to a service call fee, typically in the range of $75 to $150. If the relay board needs to be replaced, parts and labor combined can range from $200 to $500 or more depending on the specific board and local labor rates. Getting a diagnosis from a Dacor-authorized technician will give you a more accurate estimate for your model.

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