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Error code reference

A.O. Smith Water Heater Error Code 031

Incorrect dipswitch settings on the computer board.

A.O. Smith codesA.O. Smith water heater codes

Incorrect dipswitch settings on the computer board.

First step from the service manual

Turn off power supply, remove front cover, and check dipswitch settings on left and right banks against correct positions.

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

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What 031 means on a A.O. Smith water heater

Error code 031 on an A.O. Smith water heater indicates that the computer board has detected an incorrect dipswitch configuration. The control board uses a set of small binary switches, arranged in left and right banks, to identify the unit's operational parameters such as BTU input, fuel type, tank size, and venting configuration. When the board reads a switch combination that does not match an expected valid configuration, it triggers code 031 and halts normal operation to prevent running with mismatched settings.

This error most commonly appears after a control board replacement, a service visit, or any time the front cover has been removed and the dipswitches were accidentally disturbed. Each switch position is critical: a single switch in the wrong position can produce an invalid configuration that the board will not accept. The left bank and right bank of switches each control different parameters, so both must be verified against the correct positions for the specific model being serviced.

Diagnosing this error requires turning off power to the unit, removing the front cover, and carefully comparing the current switch positions on both banks against the correct settings for that unit. The correct configuration is typically found on a label inside the unit or on the board itself. No components need to be replaced in most cases unless a switch is physically damaged or the board itself is faulty and misreading a valid switch configuration.

Source: manufacturer service documentation.

Common causes of 031

  1. 01

    Dipswitches disturbed during service

    Wiring / connection

    Removing or reinstalling the front cover can accidentally shift one or more dipswitches. Carefully inspect both the left and right switch banks for any position that differs from the required configuration for the model.

  2. 02

    Incorrect settings after control board replacement

    Wiring / connection

    When a new control board is installed, the dipswitches must be manually configured to match the unit's specifications. If the replacement board was not set up correctly, code 031 will appear on first startup.

  3. 03

    Switches set to an invalid combination

    Wiring / connection

    Not all possible switch combinations correspond to a valid unit configuration. If switches are set to a combination the board does not recognize, the error will trigger even if the individual switch positions look intentional.

  4. 04

    Physically damaged or stuck dipswitch

    Part replacement

    A switch that is broken, stuck between positions, or not making proper contact will cause the board to read an incorrect configuration. Inspect each switch closely for physical damage or an ambiguous intermediate position.

  5. 05

    Faulty control board misreading valid switch settings

    Part replacement

    In rare cases, the control board itself may fail to correctly read the switch inputs even when the dipswitches are set properly. If all switch positions are confirmed correct and the error persists, the board may need to be replaced.

See the test procedure for each cause

Frequently asked questions about 031

What does 031 mean on a A.O. Smith water_heater?
Error code 031 means the control board has detected that the dipswitches on the computer board are not set to a valid or correct configuration. These small switches tell the board key information about the unit's setup, and any incorrect position will trigger this fault. The unit will not operate normally until the switch positions are corrected. This is typically a configuration issue rather than a component failure.
How do I fix error code 031 on my A.O. Smith water heater?
Turn off the power supply to the unit and remove the front cover to access the control board. Locate the left and right dipswitch banks on the board and compare each switch position against the correct settings for your specific model, which are usually listed on a label inside the unit. Adjust any switches that are in the wrong position, replace the cover, restore power, and check whether the error clears. If the switches are all correct and the error remains, a faulty board may be the cause.
Is error code 031 on an A.O. Smith water heater a safety issue?
The unit is designed to stop normal operation when it detects an invalid dipswitch configuration, which is a protective measure to prevent running with incorrect settings. While the error itself is a configuration fault rather than a dangerous condition, you should not attempt to bypass it or force the unit to run without correcting the switch positions. Restore the correct configuration before returning the unit to service.
Will resetting the water heater clear error code 031?
A simple power reset will not permanently clear code 031 if the dipswitches remain in incorrect positions. The board checks the switch configuration on startup, so the error will return each time power is restored until the switches are set correctly. The underlying configuration must be corrected first for the reset to result in normal operation.
How much does it cost to repair error code 031 on an A.O. Smith water heater?
If the fix only requires adjusting the dipswitch positions, the repair cost is limited to a service call fee, which typically ranges from $75 to $150 depending on your location and the technician. If a damaged dipswitch or a faulty control board needs to be replaced, parts and labor costs can range from $150 to $400 or more. In many cases this is a straightforward configuration correction that does not require any replacement parts.

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