Direct answer: When a water heater burner will not ignite, the usual causes are a blown-out pilot, the gas supply being off, a tripped safety reset, or a dirty burner intake area. Start with the visible checks and relight procedure, not parts.
Most likely: On a standard gas tank water heater, the most common real-world pattern is a pilot that is out or will not stay lit because the burner area is dirty or the safety circuit is not proving flame.
First separate what kind of heater you have. This page fits a gas tank water heater with a burner compartment. If you have an electric water heater, there is no burner to ignite. If you have a tankless unit showing an error or going cold mid-use, you are on the wrong problem. Reality check: a lot of 'burner won’t ignite' calls turn out to be a pilot issue, not a bad major part. Common wrong move: holding the pilot button over and over without checking for gas smell, intake blockage, or a damaged sight glass area.
Don’t start with: Do not start by replacing the gas valve or ignition controls. Those are higher-risk, higher-cost guesses and they are not the first thing to fail on most homeowner calls.
You try to start it and never see flame through the sight glass. The water stays cold and the burner never comes on.
Start here: Start by confirming this is a gas tank water heater, then check the gas shutoff position and the relight instructions on the label.
You can get a small flame briefly, but it dies as soon as you release the button or shortly after.
Start here: Focus on a weak flame-proving path first: dirty burner area, intake restriction, or a failing pilot safety component.
The control shows no normal heartbeat light, or it flashes a fault pattern while the burner stays off.
Start here: Read the label on the heater for the flash pattern, then inspect for simple causes like low gas supply, reset issues, or a dirty intake before assuming a control failure.
There is a raw gas smell around the burner compartment or control area, with or without ignition attempts.
Start here: Stop immediately. Do not relight it. Leave the area, shut off gas only if you can do it safely, and call the gas utility or a qualified pro.
This is the most common reason a gas tank water heater burner will not light. No pilot means the main burner has nothing to ignite from.
Quick check: Look through the sight glass during the relight procedure. If you never see a steady pilot flame, stay on the pilot and gas-supply checks.
A bumped shutoff valve, recent gas work, or low supply can leave the heater dead with no burner flame.
Quick check: Make sure the manual gas shutoff is parallel with the gas pipe and other gas appliances in the home are working normally.
Dust, lint, and debris can choke airflow and keep the pilot or burner from lighting cleanly or staying lit.
Quick check: Inspect the lower intake screen and burner compartment area for lint, pet hair, or dust buildup without taking apart gas components.
If gas is on, the intake is clear, and the pilot still will not light or stay lit, the heater may not be proving flame correctly.
Quick check: If you get repeated failed relight attempts with proper gas supply and a clean intake, stop short of gas-valve guessing and move to professional service.
A lot of wasted time comes from treating an electric or tankless heater like a gas tank heater. This page only fits a unit with a burner compartment and pilot or ignition assembly.
Next move: If you confirmed it is a gas tank water heater, continue with the gas and pilot checks. If it is electric, troubleshoot it as an electric no-hot-water problem. If it is tankless, use the tankless symptom that matches what it is doing.
What to conclude: You avoid chasing burner problems on a heater that does not use a burner.
Gas smell, soot, scorch marks, or a damaged burner compartment changes this from a homeowner reset to a safety call.
Next move: If the area is safe and clean-looking, you can move on to the simple ignition checks. If you smell gas or see signs of combustion trouble, stop and call a qualified pro.
What to conclude: A burner that will not ignite is one problem. A burner area showing gas leakage or combustion damage is a different and more serious one.
The shutoff valve position and control sequence are the two most common no-ignite misses. One wrong knob position can make the heater look dead.
Next move: If the pilot lights and stays lit, the burner should fire when the tank calls for heat. Let the heater run and verify hot water returns. If you never get a pilot flame, or it lights but drops out right away, move to the intake and burner-area inspection.
Dust and lint around the lower intake are common field finds, especially in garages, laundry areas, and utility rooms. Restricted air can keep the pilot or burner from lighting cleanly.
Next move: If the pilot now lights and stays lit, poor airflow or debris was likely the issue. Keep the area clear and monitor the next few heating cycles. If the pilot still will not light or hold after the gas and intake checks, the problem is likely inside the ignition or flame-proving assembly and is no longer a good guess-and-buy repair.
Once the easy checks are done, the remaining causes are usually pilot assembly, thermopile or thermocouple style safety parts, ignition components, or the gas control itself. Those are not good blind purchases on a water heater.
A good result: If service confirms a simple pilot-related repair, you can decide whether the repair cost makes sense for the age of the heater.
If not: If the technician finds combustion damage, gas valve trouble, or unsafe venting, follow the repair or replacement recommendation instead of forcing more restarts.
What to conclude: At this point you have already ruled out the common homeowner-fix items. The next step is accurate diagnosis, not more retries.
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Usually because there is no stable pilot flame, the gas is off, the control sequence is wrong, or the burner intake area is dirty enough to interfere with ignition. Start with the shutoff valve position, the label instructions, and a clean intake area.
That usually points to a flame-proving problem. The pilot flame may be weak, the burner area may be dirty, or the water heater may have a failing thermocouple or thermopile style safety component. That is a much more likely pattern than a random major control failure.
No. A couple of careful attempts following the label is reasonable if there is no gas smell. Repeated attempts without stopping can let gas build up and can hide a real combustion or control problem.
Not as a first move. Gas valves and ignition controls are expensive, fitment-sensitive, and not good guess parts. Rule out the pilot, gas supply, and intake blockage first, then get a proper diagnosis if it still will not light.
That tells you the house gas supply may be generally available, but it does not prove the water heater itself is getting gas or proving flame correctly. The local shutoff, control position, pilot assembly, and burner area can still be the problem.
No. Electric water heaters do not have a burner or pilot. If your electric unit has no hot water, the likely causes are power, elements, thermostats, or resets instead.