When the pilot light on a gas water heater goes out, the cause is usually a worn thermocouple or flame sensor, a draft, a dirty pilot orifice or a partly blocked vent. A pilot that goes out once after a gas interruption or a strong draft can be relit by following the instructions printed on the heater's label. A pilot that will not light, or that keeps going out, points to a failing part and needs a technician.
Why did the pilot light on my water heater go out?
A gas water heater pilot goes out for one of two reasons: something disturbed or interrupted the flame, or the safety system shut the gas off because it believed the flame was gone. The first group is often a one-time event. The second group repeats until the failing part is replaced.
| Cause | Typical one-time or repeating? | What it looks like |
|---|---|---|
| Gas supply interrupted (outage, utility work, empty propane tank) | One time | Every gas appliance in the house is affected, and the pilot relights normally once gas returns |
| Strong draft or downdraft through the vent | One time or repeating | Pilot goes out in windy weather, or when a range hood, dryer or bathroom fan runs |
| Worn thermocouple or flame sensor | Repeating | Pilot lights, holds while you press the button, then goes out soon after you let go |
| Dirty or partly clogged pilot orifice | Repeating | Small, weak or flickering pilot flame that struggles to heat the sensor |
| Partly blocked vent or poor combustion air | Repeating | Pilot or burner goes out after the unit has been running, sometimes with soot or a yellow flame |
| Failing gas control valve | Repeating | Pilot is healthy and the sensor tests fine, but it still will not hold |
How to check the pilot light on a water heater
On most gas storage tanks you can check the pilot without touching anything. Look at the small viewing window, usually near the bottom of the unit behind a removable access cover, and compare the flame to the table below. If the cover will not come off easily, or you are unsure what you are seeing, call instead of forcing it.
| What you see | What it usually means |
|---|---|
| A steady, mostly blue flame touching the tip of the thermocouple | A healthy pilot |
| No flame at all | The pilot is out, so the heater cannot make hot water until it is relit or repaired |
| A small, weak or flickering flame that does not reach the thermocouple | A dirty pilot orifice, a draft, or low gas pressure |
| A yellow, orange or sooty flame | Poor combustion, which can mean a venting problem and needs prompt professional attention |
| No visible window and a display with codes or lights | An electronic ignition heater with no standing pilot; see the section below |
Water heater pilot light won't light: what to check first
If the pilot refuses to light at all, work through the simple items before assuming a failed part. None of these requires opening the unit.
- Check the gas control position. The control must be in the position the label specifies for lighting, usually marked PILOT, and pushed in or held as the label directs.
- Confirm gas is reaching the house. If the range or furnace is also dead, the problem is the gas supply, not the heater. Propane users should check the tank level.
- Check the shutoff valve on the gas line. The handle should run in line with the pipe when the valve is open.
- Listen for the igniter. On units with a push-button igniter, a clear click and a visible spark mean the igniter works. No spark means the igniter is the likelier problem.
- Hold the control for the full time the label specifies. Releasing early is the most common reason a pilot that did light drops out immediately.
If the pilot lights while you hold the control and goes out as soon as you let go, the thermocouple is the prime suspect. If it will not light at all after these checks, stop and call a technician.
The safe steps to try once, in order
- Find and read the lighting instructions printed directly on your heater's own label. Steps and wait times genuinely differ between manufacturers and models, so use the ones for your specific unit rather than general instructions from memory.
- Set the gas control to the position the instructions specify before you begin, and follow each step in the order given.
- Hold the ignition button for the full time the label specifies. This lets any residual gas clear and gives the thermocouple time to heat up properly.
- If the pilot lights and holds, watch it for several minutes to confirm it stays lit on its own once you release the control.
- If it goes out again once you release the control, stop. Repeating the process will not fix a failing thermocouple, gas valve or venting problem, and it is not a situation to keep retrying.
Pilot light goes out every few days or keeps going out
A pilot that goes out repeatedly is telling you something specific, and the timing narrows down the cause.
| When it goes out | Most likely cause |
|---|---|
| Seconds after you release the control | A worn thermocouple or flame sensor, or a pilot flame too weak to heat it |
| A few minutes after lighting, once the burner has run | Poor venting or combustion air, which can trip a safety device |
| Every few days, with no obvious pattern | A marginal thermocouple, a pilot orifice that is partly clogged, or an intermittent draft |
| Whenever it is windy, or the dryer or exhaust fan runs | Draft or a competing air demand in a closet or utility room |
| After a power or gas outage | A one-time interruption; relight once and watch it |
Relighting it each time and moving on is a poor plan. A heater that is losing its pilot every few days is also losing hot water at unpredictable moments, and the underlying cause, whether a sensor or a venting problem, does not improve on its own.
Pilot light is on but the gas water heater is not working
A healthy pilot with no hot water means the pilot is not the problem. The gap is between the pilot and the main burner. Common causes are a thermostat setting that has been turned down, a failing gas control valve that does not open the main burner circuit, a clogged burner orifice or burner ports, a thermopile that is too weak to power the valve on millivolt systems, or a gas supply that supports the pilot but not the full burner. Heavy sediment can also make a working burner seem ineffective by insulating the water from the heat. Our guide to why a water heater is not heating walks through the checks by heater type, and our gas water heater repair page covers the burner and gas valve work in detail.
Water heater burner or flame keeps going out
If the main burner flame, not just the pilot, drops out while the unit is heating, treat it as a combustion problem until a technician proves otherwise. Causes include a blocked flue or vent, a clogged air inlet, a flame sensor that has failed, or a safety switch responding to flames rolling out of the combustion chamber. Many newer heaters have a sealed combustion chamber with an air inlet screen that collects dust and lint over time, and a restricted inlet can shut the unit down. Do not bypass or reset safety switches repeatedly, and do not run a heater that is producing soot or a yellow flame.
What a thermocouple does, and why it fails
A thermocouple is a small sensor that sits in the pilot flame. As long as it stays hot from that flame, it sends a tiny electrical signal that holds a safety valve open, allowing gas to reach the pilot and, eventually, the main burner. This is a deliberate safety design: if the pilot goes out for any reason, the thermocouple cools within seconds and shuts the gas valve automatically, so unburned gas cannot keep flowing into your home. Over years of repeated heating and cooling cycles, the thermocouple's connection can loosen or the sensor itself can weaken, so it stops registering the flame reliably even though the pilot is genuinely lit. That is why a pilot that will not stay lit is so often a sensor problem rather than a flame problem.
Newer heaters may not have a visible pilot at all
Many newer gas water heaters use electronic ignition instead of a standing pilot flame, and rely on a hot surface igniter or an electric spark rather than a small flame that burns continuously. These units typically show a numbered or lettered error code or a blinking light pattern instead of a simple pilot window. If yours is one of these, note the exact code or blink count along with the model number before you call, since that narrows down the likely cause immediately and often points straight to the sensor, igniter or gas valve responsible.
A water heater is also a different appliance from a boiler that heats the home. If the pilot that went out belongs to a heating boiler, follow that boiler's own manual and have a heating technician look at it. This guide covers gas storage tank water heaters.
When to stop and call a technician
- The pilot goes out a second time after you have followed the lighting instructions once.
- The pilot will not light at all after the checks above.
- The flame, once lit, looks yellow, orange or sooty rather than the mostly blue color of a healthy burner.
- You notice soot or a scorched appearance around the top of the unit or its draft hood.
- The heater sits in a small closet, or has ever had a documented venting problem in the past.
- You have any doubt at all about what you are looking at. A thermocouple replacement is inexpensive; a missed venting problem is not something to guess about.
How this connects to other water heater problems
A pilot that won't stay lit is one of several ways a gas heater shows it is not heating; the fuller picture, including electric, tankless and heat pump failure patterns, is in our guide to why your water heater isn't heating. If the same unit has also started popping or rumbling, sediment buildup near the burner area may be part of the picture too, covered in water heater noise causes. A yearly service catches many of these problems early, and the full list of tasks is in our annual water heater maintenance checklist.
Frequently asked questions
Why won't my water heater pilot light stay lit?
A water heater pilot light won't stay lit when the thermocouple or flame sensor cannot confirm the flame, so the safety valve closes and shuts off the gas. A worn sensor is the usual culprit, followed by a draft, a dirty pilot orifice or a venting problem.
What does it mean when the pilot light is out on a water heater?
The heater cannot make hot water until the pilot is relit or repaired. If gas was interrupted or a draft blew it out, one careful relight following the label may be enough. If the pilot light went out again, a part has failed.
Why do water heater pilot lights go out?
The common reasons are a worn thermocouple, a draft or downdraft, a dirty pilot orifice, a partly blocked vent, a failing gas control valve, or an interrupted gas supply. Each leaves a different pattern, described in the tables above.
Why does my water heater pilot light keep going out?
The most common reason is a worn thermocouple or flame sensor that no longer registers the flame. Drafts, a partly blocked vent, a dirty pilot orifice and a failing gas control valve cause the same symptom. The timing of when it goes out helps tell them apart.
Is it safe to relight my own pilot light?
Following the manufacturer's printed instructions on the label is generally fine for a single attempt. If the pilot will not stay lit, or you have ever smelled gas near the unit, stop and call a technician rather than repeating the process.
How do I know if the thermocouple is bad?
The classic sign is a pilot that lights and holds while you press the control, then goes out within seconds to minutes of releasing it. A technician confirms it by measuring the sensor's output rather than guessing.
How long does a thermocouple replacement take?
It is typically a same-visit repair once a technician has confirmed that is the actual cause, along with checking venting and gas pressure at the same time.
Can a bad pilot or thermocouple cause a carbon monoxide problem?
The thermocouple itself is a safety device, not a source of carbon monoxide. However, a blocked vent or poor combustion, which can produce similar symptoms, absolutely can. Working carbon monoxide alarms in the home are essential regardless of the specific cause.
Why is my gas water heater not lighting at all?
If a gas water heater will not light, check that the gas control is in the lighting position, the gas shutoff valve is open and the house has gas. No spark from a push-button igniter points to the igniter. If none of those explain it, a technician should test the gas control valve and thermocouple.
Why does my hot water tank pilot not stay lit or the flame keep going out?
A water heater flame that keeps going out, whether the small pilot or the main burner, comes from a sensor that fails to register the flame, a draft, restricted combustion air or a blocked vent. The burner section above explains why a flame that drops out under load needs prompt attention.
What does water heater pilot light repair involve?
A technician checks the gas supply and venting, tests the thermocouple, cleans the pilot assembly and pilot orifice, and tests the gas control valve. The most common fix is a new thermocouple, completed in one visit, followed by a full heating cycle to confirm the pilot holds.
Do you repair every brand of gas water heater?
We service the major brands, including Rheem, A. O. Smith, Bradford White and State. Have the model number from the rating label ready when you call so we know what parts to bring.
Full detail on gas water heater repair, including burner and gas valve issues beyond the pilot itself, is on our gas water heater repair page. If your hot water is out right now, see emergency water heater repair; we take these calls 24/7 across Lake Stevens.