A water heater that won’t ignite usually points to gas supply issues, a bad sensor, or an ignition fault—start with fuel, flame, and safety locks.
Cold shower, blinking status light, no flame. When a tank or tankless unit refuses to ignite, the cause is often simple: gas is off, air is trapped in the line, the igniter can’t spark, or the flame sensor isn’t proving the flame. This guide gives you clear checks, safe steps, and when to stop and call a pro. Safety comes first—if you smell gas, follow the printed warning on your unit and your utility’s rules before doing anything else.
Quick Diagnosis Cheat Sheet
Use this table to match the symptom with the likely cause and a fast action you can take. It’s a starting point, not a full teardown.
| Symptom | Likely Cause | First Action |
|---|---|---|
| No spark / no click | Dead igniter, loose lead, failed spark button | Inspect igniter lead and connection; reseat firmly. |
| Sparks, no flame | Pilot orifice clogged, gas shutoff closed, air in line | Confirm gas valve is ON; bleed air with repeated lighting tries; clean pilot orifice. |
| Flame lights, then dies | Thermocouple/flame sensor not reading flame | Check sensor position in flame; replace if weak. |
| Lights, then trips on main burner start | Pilot lifts off sensor, gas pressure dip, poor grounding | Verify pilot flame shape; check gas supply pressure; clean pilot parts. |
| Intermittent, windy closet/garage | Drafts blowing out flame | Shield from drafts; ensure proper combustion air. |
| Electronic model, no pilot by design | Hot-surface/electronic ignition fault | Follow unit’s reset/lockout instructions; service if no start. |
Safety First: When To Stop And Step Away
If you smell rotten-egg odor, hear hissing, or see soapy bubbles at a joint, leave the area and contact your gas supplier or fire department. Do not use switches or phones inside the space and do not try to relight anything until cleared. Your unit’s user manual repeats these steps in bold for a reason.
Once the space is declared safe, you can proceed with basic checks below. Many models also print lighting instructions on the jacket—follow those steps exactly for your model.
Why The Burner Won’t Ignite: Root Causes And Fixes
1) Gas Supply Not Reaching The Burner
Look at the manual shutoff near the unit; the handle should be parallel with the pipe. If the tank hasn’t run in a while, there may be air in the line. Multiple lighting attempts can purge that air safely if your model’s instructions allow it. Classic service literature lists “check gas supply / bleed air” as the first step when nothing lights.
2) Igniter Isn’t Firing
No click, no spark? On push-button systems, the lead can back out of the connector or crack at the porcelain. Unplug, inspect for carbon tracking, then reseat firmly. Some brands provide a dedicated “make sure the spark igniter is working” step with photos.
3) Pilot Orifice Or Tube Is Dirty
Dust and lint can choke the tiny pilot opening. You’ll get spark, maybe a flicker, then nothing. Cleaning the pilot orifice and hood is a standard fix in tech bulletins and repair guides. Avoid oversized drill bits—use compressed air or a fine wire sized for the orifice.
4) Flame Sensor / Thermocouple Isn’t Proving Flame
The sensor sits in the small blue flame and sends a tiny signal that keeps gas flowing. If it’s misaligned, sooted, or weak, the flame lights and then drops out when you release the knob. Guidance from service handbooks: verify position in the flame, clean lightly, and replace if readings are low.
Set The Sensor In The Flame Sweet Spot
The tip should sit in the heart of the pilot flame, not buried deep and not out at the edge. Too far in and heat spreads down the stem; too far out and it stays cool. Aim for full, steady contact at the tip.
5) Pilot Lifts Off When The Main Burner Starts
On some power-vented models, when the main burner fires, the small flame can lift off the orifice and lose “flame sense.” That triggers lockouts and repeating tries. The fix can be as simple as repositioning the igniter/sense rod and confirming gas pressure doesn’t sag when the burner opens.
6) Control Valve Or Safety Lockout
If outages are constant across attempts, tech trees often point to the gas control. Electronic boards and combination valves can fail and should be diagnosed with the brand’s specific procedure. Some bulletins call for replacement when outages are consistent.
7) Combustion Air, Lint, And Drafts
Closets and garages collect dust and negative pressure. A gust under a door, a clothes dryer pulling air, or a lint mat over the intake screen can stall ignition or blow out a small flame. Clear the intake, restore spacing around the jacket, and reduce drafts. Tech notes and safety pages point to shielding the flame and ensuring proper air.
8) No Pilot By Design (Electronic Ignition Models)
Newer units use electronic or hot-surface ignition. There’s no standing flame. If the burner won’t start, you’ll follow a different reset path and error-code tree than older tanks. The Energy Saver pages describe these ignition styles and how modern equipment handles lighting.
Step-By-Step: Safe Relight Procedure (Generic)
These steps mirror common user-manual directions. Always use the label on your unit if steps differ.
- Turn the gas control to OFF and wait several minutes to clear any unburned gas. Do not proceed if you smell gas; follow the warning block printed in your manual.
- Set the knob to PILOT. Hold the knob down to start gas flow to the pilot.
- Press the igniter repeatedly while holding the knob. Watch through the viewport for a small blue flame.
- Keep holding the knob for 30–60 seconds so the sensor heats. Release slowly. If the flame stays, turn the knob to ON. If it drops out, repeat once or twice to purge air, then move to sensor checks.
- Restore the access door and set temperature per your label. Many brands mark a “hot” setting around 120°F to reduce scald risk.
Deeper Fixes You Can Try Before Calling A Pro
Re-seat And Inspect The Igniter Lead
Power down the unit. Remove the igniter lead from its connector and check for cracks or carbon tracks. Re-seat it with a firm push and test again.
Clean The Pilot Hood And Orifice
Shut gas OFF. Remove the pilot tube and clear debris with compressed air. Wipe soot from the hood and ground strap. Reassemble and test. Bulletins list carbon on the pilot assembly as a frequent cause of dropouts.
Set The Thermocouple / Flame Sensor Correctly
Position the tip where the flame envelopes it. Only the upper portion should sit in the flame, not the entire stem. Replace if the flame is perfect but the flame-prove signal still fails.
Confirm Adequate Combustion Air
Open louvered doors, remove clutter, and clear intake screens. Drafts or starved air cause unstable flame and nuisance lockouts. Tech sheets point to flame lift and loss of rectification when air and pressure aren’t right.
When To Stop DIY And Call A Pro
- Repeated lockouts with a clean, blue pilot flame
- Measured sag in gas pressure when the main burner starts
- Evidence of a failing control valve or board
- Sooting, yellow flame, scorch marks on the burner door
- Any doubt about leak checks or venting
Brand literature advises service any time the flame is yellow, lifting, or unstable, and to replace controls that cause constant outages.
Model Differences That Change The Game
Standing Pilot Tanks
These rely on a continuous small flame and a thermocouple. They’re simple, but the pilot hardware needs to stay clean, blue, and steady. If the flame doesn’t bathe the sensor, gas shuts off.
Electronic Or Hot-Surface Ignition
No standing flame. The control runs a pre-purge, lights the burner with a spark or glowing element, then checks for flame. If it can’t prove flame, it locks out until you reset or fix the fault.
Power-Vent And Direct-Vent Tanks
These add a fan or sealed intake, which means airflow, vent length, and pressure matter. Some bulletins tie dropouts to pilot lift when the main burner starts; solving it can be as simple as repositioning the sense rod and verifying supply pressure.
Costs, Parts, And DIY Difficulty
Not every fix needs a truck roll. Here’s a simple planning table so you can decide what to try and what to book out.
| Part / Task | Typical DIY Scope | When To Hire |
|---|---|---|
| Pilot cleaning | Remove tube/hood, blow out debris, reassemble | Persistent lift-off, repeated relight failures. |
| Thermocouple / flame sensor | Swap with model-specific part; set tip in flame | No flame-prove signal with perfect flame. |
| Igniter lead / electrode | Inspect/replace cracked lead; reseat connector | No spark after lead/igniter replacement. |
| Gas control / board | Not a DIY item; calibration and leak checks needed | Constant outages or fault codes. |
| Combustion air / vent checks | Clear screens, open louvers, remove storage nearby | Power-vent pressure or length issues. |
Make Your Fix Safer With Two Must-Read References
Every tank or tankless model ships with a bold warning block about gas leaks and relighting. The “WHAT TO DO IF YOU SMELL GAS” section outlines the do-and-don’t list used by service techs as well.
For classic tanks with a standing flame, the A. O. Smith service handbook shows the basic tree: confirm gas supply, purge air, test the thermocouple, and verify the control. Even if you own a different brand, the sequence mirrors what most techs run in the field.
Pro Tips That Prevent Repeat No-Light Calls
Keep The Flame Blue
A steady blue pilot says the mix is right. Yellow tips, lifting, or drifting mean service. Tech bulletins flag this as a trigger for lockouts and nuisance trips.
Mind Drafts And Storage
Leave clearance around the jacket and keep solvents, paints, and rags away from the burner zone. Drafts and fumes near the floor can cause trouble in garages and utility rooms.
Know Your Ignition Type
If your unit has no tiny flame and uses electronic ignition, follow the error code chart on the label. The fix path is different from older tanks with a standing flame.
FAQ-Style Clarifications (No Fluff)
Is It Safe To Try Multiple Lights In A Row?
Yes—if your label allows it and there’s no gas smell. Many manuals tell you to turn the control OFF, wait, then retry. If the flame won’t hold after a few tries, stop and service the sensor and pilot hardware.
How Long Should I Hold The Knob?
Thirty to sixty seconds is common so the sensor heats and can keep gas flowing after you release. If it drops out, repeat once and then check position and cleanliness of the sensor.
What If My Unit Has No Little Flame Window?
That likely means electronic ignition. Follow the brand’s lockout/reset steps and use the error code list on the jacket or in the manual.
Bottom Line: Light The Flame, Prove The Flame, Keep It Stable
Every successful start needs three things: fuel reaching the burner, a spark or hot surface to ignite it, and a sensor that confirms the flame. Work through gas supply, pilot orifice, and sensor position first. If the flame lifts when the burner starts, look at air and pressure. If outages are constant after those checks, a control or board may be the culprit and a licensed tech is the next step.