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Error code reference

A.O. Smith Water Heater Error Code 8

Open ignitor circuit.

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

Open ignitor circuit.

First step from the service manual

Check all wiring to the hot surface ignitor.

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

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What 8 means on a A.O. Smith water heater

Error code 8 on an A.O. Smith water heater indicates an open ignitor circuit, meaning the control board has detected a break in the electrical circuit that powers the hot surface ignitor (HSI). The HSI is a silicon nitride or silicon carbide element that heats to approximately 2500°F to ignite the gas burner. During the ignition sequence, the control board sends voltage to the ignitor and monitors current flow. If no current is detected, the board flags an open circuit fault and locks out the ignition attempt.

The most common cause of this fault is a failed hot surface ignitor itself. Over time, the ignitor element becomes brittle and can crack, breaking the conductive path and creating an open circuit condition. Physical damage from thermal cycling, rough handling, or age-related degradation are all contributing factors. A broken ignitor will typically show infinite resistance when measured with a multimeter, confirming an open circuit.

Wiring issues are the second major category of causes. The diagnostic procedure begins with a thorough inspection of all wiring connected to the ignitor, including the harness connectors, wire terminals, and any inline connections between the control board and the ignitor. A loose connector, corroded terminal, or chafed wire can interrupt the circuit just as completely as a failed ignitor element. Resistance and continuity checks at each point in the circuit help isolate whether the fault lies in the ignitor itself or in the wiring path leading to it.

Source: manufacturer service documentation.

Common causes of 8

  1. 01

    Failed hot surface ignitor

    Part replacement

    The ignitor element has cracked or broken internally, creating an open circuit. A multimeter check across the ignitor terminals will show infinite or no resistance, confirming the element is broken.

  2. 02

    Loose or disconnected wiring connector

    Wiring / connection

    The harness connector at the ignitor or control board has come loose, interrupting the circuit. Inspect all connectors along the ignitor wiring path and reseat any that are not fully engaged.

  3. 03

    Corroded or damaged wire terminals

    Wiring / connection

    Terminal corrosion or heat damage at the ignitor connector can increase resistance to the point of an open circuit. Look for discoloration, pitting, or oxidation at the terminal contacts.

  4. 04

    Chafed or broken wire in the ignitor harness

    Wiring / connection

    A wire in the ignitor circuit may have worn through its insulation and broken the conductor inside, especially near routing points where the harness contacts the cabinet or burner assembly.

  5. 05

    Faulty control board ignitor output

    Part replacement

    If the ignitor and all wiring test good, the control board may not be supplying voltage to the ignitor circuit. This is the least common cause but should be considered after all other components have been ruled out.

See the test procedure for each cause

Frequently asked questions about 8

What does 8 mean on a A.O. Smith water_heater?
Error code 8 on an A.O. Smith water heater means the control board has detected an open circuit in the hot surface ignitor system. This tells the unit that the electrical path to the ignitor is broken, either because the ignitor itself has failed or because of a wiring problem. The heater will not attempt to light the burner while this fault is active.
How do I fix error code 8 on my A.O. Smith water heater?
Start by inspecting all wiring and connectors leading to the hot surface ignitor, reseating any loose connections and looking for damaged or corroded terminals. If the wiring checks out, test the ignitor itself with a multimeter for continuity. A reading of infinite resistance confirms the ignitor element is open and the part needs to be replaced. If both the wiring and ignitor test good, the control board output should be evaluated.
Is error code 8 on an A.O. Smith water heater dangerous?
Error code 8 is not an active safety hazard because the unit is preventing ignition rather than allowing an unsafe condition. The heater has shut itself down as intended. However, you should not attempt to bypass the lockout or manually ignite the burner, as the ignition control system exists to prevent unburned gas from accumulating.
Will resetting my A.O. Smith water heater clear error code 8?
A reset may temporarily clear the fault display, but if the underlying open circuit condition still exists, the error will return as soon as the unit attempts to ignite. Resetting is useful for confirming whether a fault is persistent, but it does not repair a broken ignitor or damaged wiring. The root cause must be corrected for the unit to operate normally.
How much does it cost to repair error code 8 on an A.O. Smith water heater?
If the repair only involves reseating a loose connector, there may be no parts cost at all, just the cost of a service call if you hire a technician. Replacing a failed hot surface ignitor typically costs between $20 and $80 for the part, with labor adding $75 to $200 depending on your area and service provider. A control board replacement, if needed, can range from $100 to $300 or more for the part alone.

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