If an AO Smith water heater won’t light, check gas supply, status light/ignition parts, and clean the air intake and flame arrestor.
Cold shower, blinking LED, no flame—this guide gets you from “no ignition” back to hot water. You’ll learn the fast checks, the parts that cause most no-light events, and the exact order to try fixes safely. Where a step calls for brand-specific info, you’ll see a link to the official material so you can match the instructions to your model.
Start With Safety And Model Details
Stand near the heater and sniff. If you smell gas, don’t relight. Turn the gas control to OFF, step outside, and call your gas utility. If no odor, move on. Grab a quick photo of the data plate and the control valve face so you can reference model numbers and control type (Honeywell/White-Rodgers/Intelli-Vent).
AO Smith hosts manuals and status-light charts for current and older units in the Owner Center. Use your model number to pull the exact guide you need on the product support page. That page lists relight steps, LED meanings, and parts layouts straight from the manufacturer.
When Your AO Smith Pilot Won’t Ignite: Quick Steps
Work top-down. You’re trying simple items first, then moving to service parts only if needed.
- Confirm gas supply. Is the manual shutoff valve inline with the pipe? If you have other gas appliances, do they run?
- Relight exactly as labeled. Follow the lighting instructions on the heater’s sticker for your control type. Give the thermocouple/thermopile 30–60 seconds on the pilot flame when prompted.
- Watch the status light. After a relight try, note the blink pattern or any error text on the control.
- Clean the air path. Vacuum lint from the base, filter, and flame arrestor. A clogged intake starves the burner and pilot.
- Check the pilot view. Look through the sight glass. A strong blue pilot that wraps the sensor is the goal. A weak, yellow, or drifting flame points to a dirty pilot or poor air.
- Retry after purging air. If gas service was recently off, air may be in the line; two or three lighting attempts may be needed (with rests between tries).
Fast Checks And What They Mean
| Symptom | What To Check | Why It Stops Igniting |
|---|---|---|
| No blink / no click | Gas control set to OFF or low thermopile output | Control won’t open gas valve without power from the thermopile |
| Clicks, no flame | Gas supply, pilot orifice, igniter | No gas at pilot, clogged orifice, or bad spark/hot-surface igniter |
| Pilot lights, won’t stay | Thermocouple/thermopile seating and flame coverage | Sensor not heated; safety drops gas once you release the button |
| Weak, lazy flame | Dirty intake filter or flame arrestor | Restricted air lowers flame quality and stability |
| LED shows ignition fault | Status code in manual | Control saw no flame or lost flame during trial |
| Works, then trips | Vent/draft, FV sensor, high-temp cutoff | Spillage, vapors, or overheating forces shutdown |
What The Parts Do (So Your Fixes Stick)
Thermocouple Or Thermopile
This probe sits in the pilot flame and creates a small voltage that keeps gas flowing. If the tip isn’t engulfed by a steady blue pilot or the connection is loose at the gas valve, the valve closes and the flame dies. AO Smith’s maintenance guide explains how the self-powered gas valve uses that thermopile output to run the control; see the maintenance & troubleshooting guide.
Igniter (Spark Or Hot-Surface)
Piezo spark types click and flash at the pilot hood; electronic spark types tick rapidly. Hot-surface styles glow red. No spark or glow? Check the wire connection and look for cracks on the igniter. Many AO Smith manuals list the test points and expected readings for your control type.
Gas Control Valve
The control sets pilot, ignition timing, and burner operation. Status lights and error codes live here. If the code points to sensor input issues, work the free fixes first (air path, flame shape, wiring, re-seat connections) before assuming the valve is bad.
Air Intake Filter And Flame Arrestor
Laundry rooms and basements shed lint and dust that compact onto the base screen and the flame arrestor plate. That strangles combustion air and leads to weak flame or no light. AO Smith issued a technical bulletin for cleaning: use a flexible brush and a vacuum through the intake slots; see the official FVIR flame arrestor cleaning instructions (PDF).
Flammable Vapor (FV) Sensor
If the sensor detects flammable vapors, ignition is blocked until conditions are safe. Many models log a fault for this state. The installation & use guide explains FV safety behavior and where to find the troubleshooting section for your unit.
Detailed Step-By-Step: Clean Air Path And Try Again
You can clear many no-light cases by restoring airflow. Here’s a safe method that mirrors the bulletin mentioned above:
- Set the gas control to OFF. Let the burner compartment cool.
- Remove the outer door or base screen as your model allows.
- Vacuum around the base and any snap-in filter. Rinse a removable filter and dry fully.
- Feed a flexible brush through the intake slots to scrub the flame arrestor. Withdraw the brush and vacuum the debris. Repeat until the brush comes out clean.
- Reinstall parts. Restore gas. Follow the relight sticker for your control type.
If the pilot is back to a firm, blue cone that hugs the sensor, you should get a steady LED and burner light-off soon after the call for heat.
Status Lights: Read Them Like A Pro
Older Intelli-Vent controls use explicit text/LED patterns; newer self-powered valves use blink counts. Both styles point you toward a system—ignition, flame sense, overheat, or sensor lockout. When you see a pattern, match it to the chart in your exact manual. A quick reference chart appears in AO Smith’s Intelli-Vent literature here: Intelli-Vent troubleshooting guide (PDF). For current residential atmospheric models, use the Owner Center link above to pull the correct blink table for your model number.
Fix Order That Works
1) Gas And Flame Basics
- Gas cock inline, supply on, and other gas appliances running.
- Strong pilot flame that fully washes the sensor.
- No drafts blowing at the burner door; close nearby doors and vents for a test.
2) Clean And Reseat
- Vacuum filter and arrestor; brush as needed.
- Reseat push-on spade connectors at the gas valve and sensor harness.
- Retighten the thermocouple/thermopile connection. Hand-snug plus a touch.
3) Recheck Codes And Relight
- Set control to PILOT/IGNITE and follow the sticker steps exactly.
- Hold the pilot button long enough to heat the sensor (often 30–60 seconds).
- Release and watch the LED. If it stays steady or blinks “normal,” call for heat.
Common Sticking Points And Simple Wins
Air in the gas line after an outage can delay the first light. Two to three careful lighting attempts with rests can clear air. Thermopile output grows with time on flame; a short hold may not build enough voltage. Dirty pilot orifice gives a thin, mis-aimed flame; a pro can clear it quickly. Laundry lint builds fast; monthly vacuuming near the base keeps the intake clear.
Relight Directions: Where To Find The Exact Sequence
AO Smith prints the relight steps on the heater’s label and in each model’s manual. Follow the steps for your exact control. If your sticker is unreadable, pull the correct manual using the Owner Center link above. You’ll see timing, knob positions, and LED expectations written for your model.
Draft, Vent, And Room Air Checks
Back-drafting and tight rooms can mimic part failure. Hold a lit match or a smoke pencil at the draft hood after the burner lights—smoke should draw into the hood. If it spills out, open a door or window near the heater and retry. Persistent spillage calls for a licensed tech to check chimney/vent size and makeup air.
What If Codes Point To Specific Systems?
Manuals group faults into buckets. Use this table to plan your next move. It keeps parts swapping to a minimum and saves a service visit when a simple cleanup fixes it.
| Code/Condition Bucket | Where To Look First | DIY Or Pro? |
|---|---|---|
| Ignition failure / no flame proved | Pilot gas flow, igniter, flame coverage on sensor | DIY checks first; pro if no spark/glow or pilot gas |
| Flame present then lost | Draft issues, dirty arrestor, loose sensor lead | DIY cleanup & wiring; pro if venting fails draw test |
| Overheat / ECO trip | Thermostat setting, sediment, restricted flow | DIY to verify setting; pro for ECO reset/part testing |
| FV sensor trip | Vapor source in room, sensor wiring | Remove vapor source; pro if lockout persists |
| Low thermopile voltage | Pilot flame strength, connection at gas valve | DIY flame tune/clean; pro for sensor replacement |
Stepwise Checks You Can Do In Under An Hour
Clean Intake And Arrestor
Follow the bulletin’s brush-and-vac method and reassemble. Many owners see immediate improvement when the base screen was packed with lint. The linked FVIR PDF shows the tool path and photos.
Seat The Sensor Correctly
Make sure the probe tip sits in the heart of the pilot flame. If the bracket is bent or the pilot hood is mis-aimed, even a clean sensor won’t make enough voltage.
Check Igniter Lead
Pull the connector, inspect for corrosion, and push it back until it clicks. With a spark style, you should see a crisp spark at the hood during ignition. With a hot-surface type, you should see a bright glow through the glass.
When A Service Call Makes Sense
- The heater trips an FV sensor or overheat fault right after start.
- You smell gas at the valve or burner compartment.
- No spark/glow after wiring checks, or the gas valve shows repeated ignition faults.
- Venting fails the draw test with windows open.
Your tech will test thermopile millivolts under flame, verify manifold pressure, clear pilot orifices, and confirm proper draft. If a control or valve is needed, they’ll match the exact part by model number.
Upkeep That Prevents The Next No-Light
- Monthly: Vacuum around the base and wipe dust from the outer door.
- Quarterly: Inspect the intake screen and brush the arrestor if the heater lives near laundry.
- Yearly: Pull the manual, review the status code list, and test a relight to stay familiar.
- Anytime work is done: Recheck the inner door seal and screws. AO Smith’s service handbook calls out a five-point inner door inspection to keep the chamber tight.
Helpful AO Smith References
Bookmark these official documents for your model:
- FVIR flame arrestor cleaning instructions — step-by-step cleaning of the intake and arrestor.
- Intelli-Vent troubleshooting guide — status light meanings and fix paths for Intelli-Vent controls.
- Owner Center product support — pull your exact manual by model number.
Short Checklist You Can Print
- Gas cock inline and other gas appliances working.
- Control to OFF, cool down, base cleaned and arrestor brushed.
- Igniter connection seated; pilot flame blue and hitting the sensor.
- Relight per label; hold long enough to heat the sensor.
- Match LED pattern to your manual and act on the listed system.
Follow the steps above with the two linked AO Smith resources by your side. Most no-light cases come down to air supply, a weak pilot that doesn’t heat the sensor, or a simple relight timing slip. With airflow restored and the pilot hugging the probe, your status light should settle into “normal” and the burner should fire as soon as the tank calls for heat.