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Error code reference

A.O. Smith Water Heater Error Code 510

Abnormal main gas valve

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

Abnormal main gas valve — driving circuit fault for the main gas valves.

First step from the service manual

If hot water is shut off but flames are still visible through the sight glass, immediately shut off gas and power and contact Technical Service Department.

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

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  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
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What 510 means on a A.O. Smith water heater

Error code 510 on an A.O. Smith water heater indicates an abnormal condition in the driving circuit for the main gas valve. This circuit is responsible for sending the electrical signal that opens and closes the main gas valve during normal burner operation. When the control board detects a fault in this driving circuit, it triggers code 510 to alert the technician that the valve control pathway is not behaving as expected. The fault may originate in the control board output stage, the wiring harness connecting the board to the valve, or within the gas valve solenoid coil itself.

The most critical safety concern associated with this fault is the possibility of an uncontrolled gas valve condition. If the driving circuit fails in a way that holds the valve open, the burner may continue to fire even after a hot water demand has ended. A.O. Smith specifically instructs that if flames remain visible through the sight glass after hot water has been shut off, the gas supply and power to the unit must be shut off immediately, and the Technical Service Department must be contacted before any further operation or repair is attempted.

Diagnosing this code typically involves inspecting the wiring and connectors between the control board and the gas valve for damage, corrosion, or loose terminals. The solenoid coil resistance of the main gas valve should be measured and compared against specification. If wiring and the valve coil check out within spec, the control board driving circuit itself may be the source of the fault. Given the potential for an unsafe valve-open condition, this repair should be handled by a qualified technician.

Source: manufacturer service documentation.

Common causes of 510

  1. 01

    Faulty main gas valve solenoid

    Part replacement

    The solenoid coil inside the main gas valve can fail electrically, causing an out-of-range resistance reading that the control board interprets as a driving circuit fault. Testing the coil resistance across the valve terminals will reveal an open, shorted, or otherwise abnormal reading.

  2. 02

    Damaged or corroded wiring harness

    Wiring / connection

    The wiring between the control board and the main gas valve can develop broken conductors, corroded terminals, or loose connectors. Visually inspect the harness and check continuity across each wire to identify the failure point.

  3. 03

    Control board driving circuit failure

    Part replacement

    The output stage on the control board that sends the activation signal to the gas valve can fail internally. If wiring and the valve solenoid both test within spec, the control board is the likely source of the fault.

  4. 04

    Short circuit in valve wiring

    Wiring / connection

    A short between wires in the gas valve circuit can cause the driving circuit to behave abnormally and trigger code 510. Inspect the harness for chafed insulation or contact between conductors near heat sources or sharp edges.

See the test procedure for each cause

Frequently asked questions about 510

What does 510 mean on a A.O. Smith water_heater?
Code 510 indicates a fault in the driving circuit for the main gas valve. This means the control board has detected that the electrical circuit responsible for opening and closing the gas valve is not operating correctly. It can be caused by a failed valve solenoid, damaged wiring, or a faulty control board output stage. Because this fault can potentially result in the burner continuing to fire when it should be off, it requires immediate attention from a qualified technician.
Is error code 510 on an A.O. Smith water heater dangerous?
Yes, this error carries a significant safety risk. If the driving circuit fault causes the gas valve to remain open, the burner can continue burning even after no hot water is being called for. If you observe flames through the sight glass when the unit should be off, shut off the gas supply and electrical power to the heater immediately and do not restart it until a qualified technician has inspected it.
Can I reset the water heater to clear error code 510?
A simple reset is unlikely to permanently resolve code 510 because it points to a hardware fault in the gas valve driving circuit. Even if the unit restarts after a reset, the underlying problem with the solenoid, wiring, or control board remains. Given the potential for an unsafe valve condition associated with this code, the root cause must be diagnosed and repaired before returning the unit to service.
Can I fix error code 510 myself?
Basic checks such as inspecting the wiring harness for visible damage or loose connectors can be performed by a knowledgeable DIYer. However, because this fault involves the gas valve and carries a risk of uncontrolled burner operation, full diagnosis and any component replacement should be handled by a licensed plumber or certified appliance technician. A.O. Smith specifically directs that if flames are visible when they should not be, you must contact their Technical Service Department rather than attempting self-repair.
How much does it cost to repair error code 510 on an A.O. Smith water heater?
Repair costs depend on the root cause identified during diagnosis. A wiring repair or connector replacement is typically the least expensive outcome, often in the range of $75 to $200 including labor. Replacing the main gas valve generally costs between $150 and $400 depending on the model and parts availability. If the control board is the source of the fault, board replacement can range from $200 to $500 or more. A service call fee will usually apply in addition to parts and labor costs.

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