What does A.O. Smith Water Heater No Ignition - Causes & Fix mean?

Usually a failed igniter or loose igniter wiring preventing spark. Check wiring and replace the igniter if no spark is present.

How do I fix A.O. Smith Water Heater No Ignition - Causes & Fix?

Work through the step-by-step fix below. Start with the quick reset and the most common cause, then check the specific part this guide points to. Most fixes need only basic hand tools and the right replacement part.

Can I keep using my appliance with this error showing?

Usually not. These appliances show this error when a part or safety circuit is out of range, so running it can stop the cycle or make the problem worse. Diagnose and clear the error before normal use.

What part is most commonly replaced for A.O. Smith Water Heater No Ignition - Causes & Fix?

The parts that most often fix A.O. Smith Water Heater No Ignition - Causes & Fix are listed in the parts section of this guide. Match the part to your exact model and serial number before you buy.

Is A.O. Smith Water Heater No Ignition - Causes & Fix a DIY repair or do I need a technician?

Many fixes are DIY-friendly with basic tools, such as door switches, drain pumps, water inlet valves, thermostats, heating elements, and filters. Sealed-system, refrigerant, gas, or high-voltage work should go to a licensed technician for safety.

A.O. Smith Water Heater No Ignition - Causes & Fix

A.O. Smith Water Heater No Ignition — What’s Happening

No ignition means the control called for heat but the burner or pilot did not light, so no flame was established and the heater cannot warm water. On A.O. Smith gas water heaters, this is a fault condition rather than a single universal code. The exact diagnostic code (if displayed) depends on your model family, so always confirm the meaning from the rating plate or owner’s manual rather than assuming a generic code applies.

On pilot-equipped units, the control attempts to spark the pilot. If there is no spark, the problem is in the igniter circuit (igniter, wiring, or control). If there is spark but no light, the issue is usually gas supply or flow. On electronic-ignition and commercial units, ignition failure can also involve the gas valve, flame-sensing circuit, or venting and airflow problems.

Jump to Fix

Most Likely Causes

Failed or weak igniter The spark igniter or hot-surface igniter has burned out or cracked, so no spark is produced when the control calls for ignition.
Loose, damaged, or corroded igniter wiring Connections at the igniter or control board are loose, corroded, or broken, interrupting the ignition circuit and preventing spark.
No gas supply or gas valve not opening The manual gas shutoff is closed, supply pressure is low, or the gas valve fails to open even when signaled by the control.
Blockage in pilot tube, burner orifice, or passages Debris, dust, or corrosion clogs the pilot assembly, pilot tube, or burner orifice, preventing gas from reaching the ignition point.
Faulty thermopile or thermocouple (standing-pilot models) On pilot systems, the thermopile output is below 350 mV or the thermocouple fails to prove flame, preventing the gas valve from staying open.
Failed gas valve The valve does not deliver gas to the burner or pilot even when the ignition circuit and thermopile output (above 350 mV) are correct.
Venting or combustion-air problems On power-vent or high-efficiency units, blocked venting, lint buildup, or insufficient combustion air can prevent ignition or cause flame failure.

How to Diagnose and Fix

Verify the exact model and ignition type from the rating plate, and note any LED status code or flash pattern in the manual before diagnosing.
Confirm the manual gas shutoff valve upstream of the heater is fully open and that other gas appliances in the home are operating (to verify supply).
Observe an ignition attempt through the sight glass or access port and watch for a visible spark at the pilot or igniter.
If no spark is present, turn off power and gas, then inspect the igniter wiring and connectors for damage, corrosion, or loose contacts and repair any faults.
If wiring is intact but still no spark, test or replace the igniter (most igniters fail internally and show no visible spark even when powered).
If there is spark but no ignition, remove and clean the pilot tube, burner orifice, and nearby passages to clear any blockage or debris.
On standing-pilot models with spark but no light, use a multimeter to measure thermopile output at the gas-valve connector: below 350 mV means replace the thermopile, above 350 mV with secure wiring means replace the gas valve per A.O. Smith guidance.
After any repair, restore power and gas, cycle the thermostat or reset the control, and verify repeated successful ignition and stable flame before closing access panels.

Parts You Might Need

Part	Notes
Igniter (spark igniter or hot-surface igniter)	Amazon \| Model-specific. Verify part number from the rating plate or service manual before ordering.
Thermopile	Amazon \| For standing-pilot models. Replace if millivolt output is below 350 mV at the gas-valve connector.
Gas valve	Amazon \| Replace if thermopile reads above 350 mV, wiring is secure, and valve still will not open or deliver gas.

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

When to Call a Pro

If you are not comfortable working around gas piping, pilot flames, or live ignition circuits, call a licensed plumber or gas technician. All igniter replacement, thermopile testing, gas-valve work, and venting diagnostics on gas water heaters are best handled by a professional to avoid gas leaks, incomplete combustion, or unsafe operation. If you have checked wiring and confirmed gas supply but still see no spark or no ignition, a pro can test the control board, ignition module, and gas pressure accurately and replace components safely. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.