A.O. Smith Water Heater Pilot Won't Stay Lit - Causes & Fix

A.O. Smith Water Heater Pilot Won’t Stay Lit — What’s Happening

When your pilot lights but goes out as soon as you release the pilot knob, the gas control valve is not receiving the flame-sense signal it needs to keep the pilot gas flowing. A.O. Smith units use a thermocouple or thermopile that must detect the pilot flame and send a small electrical signal to hold the pilot safety valve open. If that signal is missing or too weak, the valve closes for safety.

After the pilot is lit and stable, the status light on your A.O. Smith control should flash once per second. If the pilot will not hold or the status light does not behave this way, the flame-sense circuit or another component is not working correctly.

Jump to Fix

Most Likely Causes

• Failed thermocouple or thermopile A.O. Smith specifically notes that a broken thermocouple will not send power to the pilot safety valve, so the pilot will not stay lit once the knob is released.
• Dirty or clogged pilot assembly Dust, debris, or contamination in the pilot orifice or burner area weakens or deflects the pilot flame so it cannot properly heat the thermocouple.
• Thermocouple or thermopile positioned incorrectly If the sensing element is not in the pilot flame or has been bent or moved, it will not get hot enough to generate the signal needed to keep the valve open.
• Insufficient combustion airflow around the unit A.O. Smith warns that blocked air inlets, dirty intake screens, or debris-loaded flame arrestor areas reduce combustion air and can cause the pilot to go out.
• Gas supply pressure fluctuations or interruptions Low or unsteady gas pressure, a closed manual shutoff, or a kinked or clogged flex tube will starve the pilot and prevent it from staying lit.
• Drafts from open doors or windows Air currents blowing across the burner compartment can extinguish the pilot flame or cause it to lift off the pilot hood.
• Gas control valve failure If the pilot assembly, sensing device, and gas supply are all good but the pilot still will not hold, the gas control valve itself may have failed internally and need replacement.

How to Diagnose and Fix

1. Check for any gas odor around the heater. If you smell gas, do not attempt to relight. Turn off the gas supply, ventilate the area, and call a qualified technician or your gas company immediately.
2. Verify that the manual gas shutoff valve upstream of the heater is fully open and that gas is reaching the unit.
3. Light the pilot following the manufacturer lighting instructions and observe the pilot flame. It should be steady, blue, and large enough to wrap around the thermocouple or thermopile tip. A weak, yellow, or wavering flame indicates contamination, low gas pressure, or draft.
4. Inspect and clean the pilot assembly and burner area. Remove any dust, lint, or debris from the pilot orifice, burner ports, and air intake screens or flame arrestor openings.
5. Check the thermocouple or thermopile position. The tip must sit in the outer envelope of the pilot flame. If it is bent away or not centered, reposition it so the flame engulfs the sensing tip.
6. Test for drafts by watching the pilot flame while opening and closing nearby doors or windows. Eliminate any air currents blowing into the burner compartment.
7. If the pilot flame is strong and the thermocouple is properly positioned but the pilot still will not stay lit after releasing the knob, replace the thermocouple or thermopile.
8. If a new thermocouple does not solve the problem and gas supply and airflow are confirmed good, the gas control valve has likely failed internally and should be replaced by a qualified technician.

Parts You Might Need

Related Error Codes

If your appliance also shows a code on the display, these match this problem:

• A O Smith Water Heater E2 error code
• A O Smith Water Heater E4 error code
• A O Smith Water Heater E6 error code

When to Call a Pro

If you smell gas at any time, stop immediately and call a professional or your gas utility. If you have replaced the thermocouple, cleaned the pilot and burner area, confirmed good gas supply and airflow, and the pilot still will not hold, the gas control valve or another internal component has likely failed. A.O. Smith notes that kinked or clogged flex tubes and internal gas-valve faults require a service visit and often valve replacement. Any work on gas piping, the gas control valve, or the burner manifold should be performed by a licensed technician to avoid safety hazards and code violations. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.