Ao smith water heater thermocouple gas pilot keeps going out: What to Check and What to Do Next

Use only checks that match the exact appliance or system and its official guide.

1. Check 1

   Before touching the control, check from a safe position for a gas odor, hissing, a carbon-monoxide alarm, smoke or soot, flame outside the normal viewing area, water around the heater, or a damaged vent or viewport. Do not open the combustion chamber to inspect it.

   Expected result: Any gas odor, alarm, hissing, abnormal flame, soot/scorching, water intrusion, damaged viewport, or suspected blocked vent is present; or none of these signs is present.

   Next step: If any danger sign is present, leave the area and contact the gas supplier, fire department, emergency service, or a qualified technician from a safe location. If no danger sign is present, continue without opening the inner door or disturbing gas connections.

   Stop if: Stop immediately for gas odor, a carbon-monoxide alarm, visible flame outside the chamber, scorched/discolored combustion parts, water submersion, or an unsafe vent condition.

   Why this matters

   Why: A danger sign makes relighting or diagnosis unsafe and can indicate a gas leak, combustion problem, flammable-vapor event, flood damage, or carbon-monoxide risk. The absence of a danger sign permits only the low-risk identification checks below; it does not prove the appliance is safe to repair.

2. Check 2

   Read the rating label and lighting instructions from outside the heater, and record the complete model and serial numbers, fuel type shown on the label, ignition style, and whether the control uses a thermocouple or thermopile. Do not assume that an AO Smith procedure for one heater applies to another.

   Expected result: The model, fuel type, control style, and lighting label are clear; or the label is missing, unreadable, inconsistent, or the heater's design is uncertain.

   Next step: If the identity is clear and there is no safety sign, use only that model's manual for any permitted user operation. If it is unclear, keep the gas control off and request manufacturer support or qualified service.

   Stop if: Stop if the label is damaged, the stated fuel does not match the supply, the viewport is broken, or the unit's ignition style cannot be identified.

   Why this matters

   Why: The label and model determine whether the unit has a manually lit pilot, electronic ignition, a thermocouple, a thermopile, or model-specific status codes. An uncertain identity makes a generic relighting or part recommendation unsafe.

3. Check 3

   Without removing the inner combustion door or touching the burner, observe the status light and the pilot only through the heater's intended sight glass or indicator, if present. Record whether the pilot lights but goes out immediately when the control is released, stays lit briefly and then drops out, or goes out during burner operation; record the status-light pattern without guessing its meaning.

   Expected result: The pilot is not visible, the status light does not reach the model's normal indication, a model-specific fault pattern repeats, or the pilot drops out at a consistent point.

   Next step: Write down the exact timing and status-light pattern for the technician and consult only the matching manual. Do not repeatedly relight, bypass a safety, or test sensor output or gas pressure yourself.

   Stop if: Stop after a failed or abnormal attempt, any repeated fault pattern, or any need to open the combustion door, access wiring, or expose the burner.

   Why this matters

   Why: A pilot that drops out when the control is released is consistent with insufficient sensor heat, a weak or misdirected pilot, a thermocouple/thermopile or connection fault, or a gas-control issue. A pilot that goes out during operation makes draft, combustion air, venting, flame-arrestor, gas supply, or safety-limit causes more important. The observation cannot distinguish these parts by itself.

4. Check 4

   From outside the appliance, look for boxes, lint, dust, storage, or other material blocking the heater's air-intake area or the visible vent termination. Note whether a furnace, air handler, exhaust fan, or newly closed door changes when the pilot goes out. Do not move the heater, alter venting, remove a screen, or test draft with a flame.

   Expected result: The intake or vent termination is obstructed, storage has been placed around the heater, the pilot loss coincides with another air-moving appliance, or no external airflow issue is visible.

   Next step: If an obstruction can be removed without touching the heater, clear the surrounding area only. Do not modify the vent or relocate the heater; a persistent issue or any concern about combustion air or draft requires a qualified technician.

   Stop if: Stop if the vent is damaged or disconnected, combustion parts are discolored, an appliance exhaust changes the flame, or inspection would require climbing, dismantling, or entering a confined space.

   Why this matters

   Why: AO Smith troubleshooting materials identify blocked air intake, insufficient combustion air, draft, and interactions with return-air equipment as possible pilot-extinguishing conditions. A clear exterior does not rule out a venting or combustion fault inside the system.

5. Check 5

   Verify only from the normal control position that the gas-control knob is not accidentally set to OFF and that the manual gas shutoff has not been changed, using the model label and safe access. Do not force a knob, adjust a regulator, loosen a gas fitting, or infer pressure from flame appearance.

   Expected result: The control is OFF, the manual shutoff is closed, the knob will not move by hand, the appliance fuel does not match the label, or the control and supply appear correctly positioned.

   Next step: If the control was accidentally set incorrectly and there is no gas odor or other hazard, follow the heater label's user instructions once. If the knob is stiff, fuel is mismatched, or the pilot still fails, leave the control OFF and call a qualified technician or gas supplier.

   Stop if: Stop for a stiff knob, gas odor, hissing, a suspected supply defect, any need to remove a fitting, or any need to measure or change gas pressure.

   Why this matters

   Why: An OFF control or closed supply can explain an extinguished pilot, but a stiff control or mismatched fuel is a safety/service condition. Correct position does not rule out unstable gas pressure, a blocked pilot path, a sensor problem, or a failed control valve.

6. Check 6

   Prepare a service note with the model and serial numbers, fuel type, ignition style, exact status-light pattern, pilot timing, recent installation or maintenance, nearby airflow changes, and every safety observation. State that the pilot repeatedly goes out and that the suspected component is the thermocouple or thermopile, not a confirmed diagnosis.

   Expected result: The symptom and identifying information are complete, or the heater cannot be safely observed or identified.

   Next step: Arrange qualified water-heater service for recurring pilot loss. Keep the gas control OFF until the technician confirms the appliance is safe, especially if the pilot will not stay lit after the model's normal label procedure.

   Stop if: Stop all DIY work if the next step involves removing the inner door, burner or pilot assembly, thermocouple, wiring, gas valve, vent, or flame-arrestor parts.

   Why this matters

   Why: The same pilot symptom can arise from a sensor, weak flame, gas supply, combustion air, venting, wiring, gas control, thermal safety, or flammable-vapor event. A precise service note helps the technician choose a model-correct test without bypassing safety controls.