Short answer
Most often the gas supply is off, the pilot or electronic igniter failed, or a safety device (thermocouple, flame sensor or flammable vapor sensor) shut the burner down. Confirm the gas valve is open and other gas appliances work, then follow the lighting label once. If it still will not heat, call a licensed plumber.
Key facts
- Thermocouple replacement, the most common gas tank repair, runs about $100 to $325; a gas control valve runs $150 to $550 (HomeGuide, 2025).[2]
- Rheem says repairs make the most sense on tanks under 6 to 8 years old; tanks typically last 8 to 12 years.[1]
- HomeGuide warns never to try lighting a pilot by hand on a gas water heater that has electronic ignition.[2]
First: is it safe to troubleshoot?
If you smell gas anywhere near the heater, do not touch the controls. Leave on foot, avoid anything that can spark (including your phone), and call the gas utility and 911 from a safe distance[3]. Everything below assumes there is no gas smell.
The 5-minute homeowner check
- Is gas reaching the house? If the stove or furnace also will not light, the problem is upstream: a closed meter, a utility shutoff, or an empty propane tank. Call the utility or propane supplier.
- Is the heater's gas valve open? The handle on the gas pipe beside the heater should run parallel to the pipe. Do not take apart any fitting.
- Is the control set to heat? Make sure the knob on the gas control is not on "pilot" or "vacation," and the temperature dial was not turned down.
- Read the status light. Many newer gas tanks blink a code on the control. Count the blinks and match them to the chart on the unit's label or in the manual. Write it down before you reset anything.
- Check the pilot or igniter. Older tanks have a standing pilot you can see through a small window. Newer tanks use electronic ignition with no flame between cycles. HomeGuide warns never to try lighting an electronic-ignition unit by hand[2].
If the pilot is out on a standing-pilot model, follow the lighting instructions on the unit's label once. If it lights and goes out when you release the knob, see pilot light won't stay lit. Do not keep retrying.
Causes, from most to least common
| Cause | What you see | Who fixes it |
|---|---|---|
| Gas supply off or interrupted | No appliances light, or the heater's valve is closed | Homeowner (open valve) or gas utility |
| Pilot out (standing pilot) | No flame in the window | Homeowner per label; pro if it will not stay lit |
| Failed thermocouple or flame sensor | Pilot lights but dies when the knob is released | Licensed plumber |
| Flammable vapor sensor lockout | Burner will not relight; status light shows a lockout | Licensed plumber, after removing fumes from the room |
| Failed gas control valve or thermostat | Pilot lit, burner never fires | Licensed plumber |
| Venting or draft problem | Pilot blows out, scorch marks, or a draft sensor trips | Licensed plumber (carbon monoxide risk) |
| Igniter failure (electronic models) | Clicking with no light, or no click at all | Licensed plumber |
Flammable vapor lockouts deserve a note. Gas tanks with this sensor shut down if they detect fumes from gasoline, paint, solvents or similar products stored nearby. If you keep those in the same room, move them out once you are sure it is safe, then call a pro to reset or replace the sensor. Do not try to bypass it.
Venting is the one cause with a health risk beyond the heater. A blocked or disconnected flue can push exhaust, including carbon monoxide, into the home. Scorch marks around the burner door, a flame that rolls out, or a pilot that keeps blowing out are reasons to shut the gas valve and call.
What the repair will likely cost
HomeGuide's national ranges, published August 2025, based on member-reported projects[2]:
| Repair | Typical range |
|---|---|
| Pilot light relight or replacement | $50 to $200 |
| Igniter repair | $75 to $350 |
| Thermocouple replacement | $100 to $325 |
| Flue pipe replacement | $100 to $350 |
| Gas control valve replacement | $150 to $550 |
| Typical tank repair overall | $150 to $700 |
Service call fees of $50 to $200 may apply on top[2]. Prices vary by city and by how hard the heater is to reach. These are not quotes.
Repair or replace?
Rheem's guidance: repair a tank under about 6 to 8 years old with one failed part; consider replacing at 10 years or more; and replace when the repair costs more than 50% of a new unit[1]. A gas control valve on a 12-year-old tank often fails that test. Check the build date with our age decoder before you approve a big repair.
A low-cost note for the future: a standard atmospheric gas tank burns roughly 40 therms a year just keeping the tank hot, even with no hot water use[4]. If you are replacing anyway, that standby loss is part of the tank vs tankless comparison.
When to call a pro
- The pilot will not stay lit after one or two attempts, or the burner will not fire.
- The status light shows a lockout or a flammable vapor fault.
- You see scorch marks, flame rollout, or soot near the burner door.
- Any work on the gas valve, thermocouple, igniter, burner or flue.
More questions
Why do I have some hot water but it runs out fast?
That is a different problem from none at all. On a gas tank it usually points to sediment, a broken dip tube, a thermostat set low, or a tank too small for the household. See our sizing guide and the popping noises page.
Can I relight the pilot myself?
On a standing-pilot model, the lighting steps printed on the unit are written for owners. Follow them exactly, once or twice. If you smell gas, do not try. If it will not stay lit, stop and call a plumber.
Sources
- Water heater lifespan: when to repair vs. replace (Mar 25, 2026), Rheem Manufacturing. Accessed 2026-10-06.
- Hot water heater repair cost (Aug 7, 2025), HomeGuide. Accessed 2026-10-06.
- What to do if you smell natural gas, CenterPoint Energy. Accessed 2026-10-06.
- Strategy Guideline: Proper Water Heater Selection (rev. Apr 2015), U.S. Department of Energy, Building America. Accessed 2026-10-06.
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