Can I keep running the equipment with this fault active?

Generally no. Faults on Water heater units are emitted when a sensor, safety, or control circuit is outside its operating envelope. Running through an active fault risks compressor, heater, or control-board damage. Diagnose and clear the fault first.

What part is most commonly replaced for A.O. Smith Water Heater Thermocouple Replacement - Signs & How-To?

The most frequently replaced parts for A.O. Smith Water Heater Thermocouple Replacement - Signs & How-To are listed in the Parts Reference section of this guide with OEM part numbers and typical price ranges. Check the table for direct replacements.

Is A.O. Smith Water Heater Thermocouple Replacement - Signs & How-To a DIY repair or do I need a technician?

Sensor swaps, fan motor replacements, and condenser cleaning are typical DIY-level repairs. Anything involving refrigerant, gas, or high-voltage (>240V) work requires a licensed technician for both safety and code-compliance reasons.

A.O. Smith Water Heater Thermocouple Replacement - Signs & How-To

Q: What does A.O. Smith Water Heater Thermocouple Replacement - Signs & How-To mean?

Pilot won't stay lit, or it lights briefly then shuts off. Replace the thermocouple (pilot flame sensor) to restore gas flow and heating.

Q: How do I fix A.O. Smith Water Heater Thermocouple Replacement - Signs & How-To?

Follow the step-by-step diagnosis below. The most likely fix is identified by checking power, sensor resistance, and control-board signals in order — using a multimeter and the part numbers documented in the parts reference table.

A.O. Smith Water Heater Thermocouple Replacement — What This Part Does

The thermocouple is a pilot flame sensor that sits in the pilot flame and generates a small electrical signal when heated. This signal proves flame presence to the gas control valve, which then keeps the gas valve open for the pilot and main burner. When the thermocouple fails or its tip is not properly positioned in the flame, the gas valve shuts down the pilot and main burner for safety.

Thermocouples fail when the sensor junction wears out over time, or when they become damaged, kinked, or unseated from their mounting bracket. If the pilot flame is too weak or misaligned to heat the thermocouple tip properly, the sensor cannot generate a stable signal even if it is still functional. Loose connections at the gas valve or damaged wiring during prior service also prevent the thermocouple from proving flame correctly.

Jump to Replacement Steps

Signs It Needs Replacing

Pilot lights but will not stay lit when you release the control knob The thermocouple is not generating a valid signal to hold the gas valve open, so the valve closes as soon as you stop manually holding it.
Pilot lights briefly then shuts off within seconds or minutes The thermocouple signal is weak or intermittent, so the gas control does not receive continuous flame proof.
Pilot flame is present but main burner will not fire The gas control is not receiving a stable thermocouple signal and refuses to open the main gas valve for safety.
Thermocouple tip is not positioned in the pilot flame or is bent away The sensor cannot heat properly and generate the holding signal if it is misaligned or not seated in the mounting bracket.
Visible damage, kinks, or corrosion on the thermocouple wire or tip Physical damage interrupts the sensor’s ability to generate or transmit the flame-proving signal to the gas valve.
Pilot relights normally after the thermocouple is cleaned or repositioned but still fails within hours The thermocouple junction is failing internally and cannot maintain a stable output even when properly aligned.

How to Replace It

Turn the gas control knob to OFF and shut off the gas supply valve upstream of the water heater.
Remove the outer burner tube assembly cover or manifold cover to access the combustion chamber (fasteners vary by model).
Disconnect the thermocouple lead from the gas control valve, then disconnect the pilot gas tube and any spark wire or safety thermostat wires as needed to free the burner assembly.
Remove the old thermocouple from its mounting bracket or retainer in the pilot assembly and pull it back through the grommet or opening in the burner compartment.
Insert the new thermocouple through the opening or grommet and seat it fully into the mounting bracket or retainer until it clicks or sits firmly in place.
Position the thermocouple tip so the pilot flame will cover the top 3/8 to 1/2 inch of the sensor tip when the pilot is lit.
Reassemble the burner assembly, pilot gas tube, main burner tube, spark wire, and safety thermostat wires, then reinstall the burner compartment cover and gasket.
Reconnect the thermocouple lead to the gas control valve and restore the gas supply, then relight the pilot per the manufacturer lighting instructions.
Leak-check all disturbed gas connections with soap-and-water solution while the burner is operating and confirm the pilot stays lit and the main burner fires on demand.

The Part You Need

Part	Notes
Thermocouple (pilot flame sensor)	Amazon \| Available in 24-inch and 36-inch versions depending on model. Use your water heater model and serial number (on the data plate) to find the correct OEM replacement part from A.O. Smith’s parts page or an authorized supplier.

If this part is failing you may also see one of these codes:

When to Call a Pro

Gas appliance work that involves disconnecting burner assemblies, pilot tubes, and gas valve connections is best left to a licensed technician. If you are uncomfortable working with gas fittings, cannot access the burner compartment safely, or still experience pilot shutdowns after replacing the thermocouple and repositioning the tip in the flame, call a qualified plumber or gas appliance technician. Persistent pilot issues after thermocouple replacement may point to a failing gas control valve, blocked pilot orifice, or venting problem that requires professional diagnosis and repair. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.