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Error code reference

A.O. Smith Water Heater Error Code 701

Computer board fault.

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

Computer board fault.

First step from the service manual

Turn off power supply and check all wire connections, making sure they are secure and free of burns or cuts.

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

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What 701 means on a A.O. Smith water heater

Error code 701 on an A.O. Smith water heater indicates a computer board fault, meaning the main control board has detected an internal failure or has lost the ability to properly manage water heater operations. The control board serves as the central processing unit for the appliance, coordinating ignition sequencing, temperature regulation, safety shutoffs, and communication between sensors and other components. When this board fails or experiences a fault condition, the unit will typically cease normal operation and display code 701 to alert the technician.

The fault can stem from several sources including wiring issues, power supply irregularities, or a failure within the board itself. Before condemning the control board, a thorough inspection of all wiring connections leading to and from the board is essential. Loose terminals, corroded connectors, burned wires, or cut insulation can disrupt signal paths and cause the board to report a fault condition even when the board's internal components are intact.

The first and most critical diagnostic step is to turn off power to the unit and carefully inspect every wire harness connection at the control board. Look specifically for signs of heat damage, discoloration, melted insulation, or terminals that have backed out of their housings. Restoring secure, clean connections sometimes clears the fault. If wiring checks out and the fault persists after restoring power, the control board itself is likely the failed component and will require replacement.

Source: manufacturer service documentation.

Common causes of 701

  1. 01

    Loose or disconnected wiring at the control board

    Wiring / connection

    Wire connectors at the board can loosen over time due to vibration or thermal cycling. Inspect all terminal connections for secure seating and check for any that have backed out of their housing.

  2. 02

    Burned or damaged wiring

    Part replacement

    Heat exposure, rodent damage, or an electrical event can burn or cut wires leading to the control board. Look for discoloration, melted insulation, or visible wire damage along all harnesses.

  3. 03

    Power supply irregularity

    Wiring / connection

    Voltage spikes, surges, or an unstable power supply can corrupt board operation and trigger a fault code. Verify that the supply voltage at the unit is within the rated specification for the heater.

  4. 04

    Failed control board

    Part replacement

    Internal component failure on the control board itself, such as a failed capacitor, relay, or processor, will produce a persistent 701 fault that cannot be cleared by addressing wiring or power issues. Board replacement is required in this scenario.

  5. 05

    Corrosion at board connectors

    Wiring / connection

    Moisture intrusion in the installation environment can cause corrosion on connector pins, increasing resistance and disrupting signal integrity between the board and connected components.

See the test procedure for each cause

Frequently asked questions about 701

What does 701 mean on a A.O. Smith water_heater?
Error code 701 indicates a computer board fault on your A.O. Smith water heater. The main control board has detected an internal failure or a wiring problem that is preventing normal operation. The unit will not heat water until the fault is diagnosed and resolved. The first step is to power off the unit and inspect all wiring connections at the control board for damage or loose terminals.
Can I fix error code 701 myself?
A homeowner comfortable with basic electrical safety can perform the initial diagnostic step of powering down the unit and inspecting wire connections for looseness, burns, or cuts. If tightening connections resolves the fault, no parts are needed. However, if the control board itself has failed, replacing it requires working with the unit's electrical system and is best handled by a qualified technician.
Is it safe to use my water heater while it shows code 701?
No. A 701 fault means the control board is not functioning correctly, and the water heater should not be operated until the fault is cleared. The control board manages safety functions including temperature limiting and ignition control, so operating the unit with a board fault could create unsafe conditions. Turn off power to the unit until the issue is repaired.
Will resetting the water heater clear error code 701?
A simple power reset may temporarily clear the code if the fault was caused by a transient power event, but the 701 code will return if an underlying wiring problem or board failure is present. A reset alone is not a repair. After restoring power, inspect all board connections and monitor the unit to see if the fault reappears.
How much does it cost to fix error code 701 on an A.O. Smith water heater?
If the fault is caused only by loose or damaged wiring, repair costs are typically limited to labor charges, generally in the range of $75 to $150 depending on your area. If the control board itself needs replacement, the combined cost of the part and labor can range from $200 to $500 or more depending on the specific model and local service rates.

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