Gas Water Heater Pilot Won’t Stay Lit? Troubleshooting Tips

Home » Gas Water Heater Pilot Won’t Stay Lit? Troubleshooting Tips

That hot shower you enjoy in the morning or the ability to efficiently wash the dinner dishes in the evening may be dependent on one little flame staying lit: the pilot flame at the base of your gas water heater. If the water heater pilot won’t light or won’t stay lit, you’re going to be suffering through a lot of cold showers until you can fix the problem. Not all gas water heaters use a pilot flame, but for those that do, Repair Clinic has identified the three most likely causes of that pilot not lighting or not staying lit. First, let’s examine the two different types of ignition systems gas water heaters use to heat the water.

Two different types of gas water heater ignition systems

After water enters a gas water heater tank, a burner positioned directly under the bottom of the tank will be ignited to heat the water. Some water heater models use a pilot to ignite the burner while other models rely on a hot surface ignition system to accomplish this.

How a hot surface ignition system is used to ignite the burner

A hot surface ignition system is comprised of a thermostatically-controlled gas valve along with a control board. In addition, a power vent blower fan will exhaust the fumes generated by this system to the outside of the home. When the gas valve detects a decrease in water temperature, the control board begins a timed ignition sequence by sending 120 volts of alternating current to a draft inducer fan motor which turns on to draw air into the burner. Once the draft inducer fan motor reaches its maximum speed, a pressure switch closes, and the control board sends 120 volts to the hot surface igniter. Next, the control board energizes a solenoid on the gas valve which allows gas to flow into the burner and be lit by the igniter. A flame sensor is used to monitor the burner flame to ensure it is lit while gas is flowing through the valve.

How a pilot is used to ignite the burner

On water heaters using a pilot, the pilot and burner are also regulated by a thermostatically-controlled gas valve. When the valve detects a decrease in water temperature, it opens, allowing the pilot to light the burner and the water to be heated. Most pilot systems will use either a thermocouple or thermopile (which is, essentially, several thermocouples combined in a larger casing) to monitor the pilot. If the pilot goes out, the thermocouple or thermopile will prevent the gas valve from opening. Water heater models with a thermopile will also incorporate a limit thermostat to prevent the gas valve from opening if the burner or the surrounding area gets too hot.

How a pilot can be relit

If a gas water heater pilot light goes out, it must be relit according to the water heater manufacturer’s instructions. More recent model water heaters have a pilot setting on the gas valve and a spark electrode to light the pilot. Rotate the selection dial to the pilot setting and the spark electrode should automatically light the pilot. Older water heater models will still have that pilot setting, but after selecting the setting you will need to light the pilot with a long match or lighter manually.

Three likely causes of a water heater pilot not lighting

So, why won’t your gas water heater pilot light or stay lit? Here are the three most likely causes plus some troubleshooting tips to assist in correcting the problem:

  1. Defective spark electrode – As noted above, more recent model gas water heaters use a spark electrode to automatically light the pilot flame when the pilot setting is selected. If the spark electrode is defective, the pilot won’t light. Examine the spark electrode to see if there is any corrosion at the tip. Carbon buildup can prevent the electrode from sparking properly. You may be able to use medium-grade sandpaper to clean off the buildup. If this isn’t effective, replace the corroded electrode with a new one.
  2. Restricted pilot – Carbon deposits can also create a restriction in the pilot orifice and prevent it from being able to light the burner. Try cleaning the orifice with a stiff brush or compressed air. If cleaning does not successfully restore the pilot’s ability to light the burner, you can always install a new pilot to fix the problem.
  3. Defective thermocouple or thermopile – As mentioned earlier, most pilot systems will use either a thermocouple or a thermopile to monitor the pilot. A defective thermocouple or thermopile may not be able to properly monitor the pilot flame which can result in the flame going out. Both thermocouples and thermopiles can be tested with a multimeter that can read millivolts DC. You will need to hold the tip of the component over a flame with the black meter lead in contact with the top end of the thermocouple or thermopile and the red meter lead in contact with the tubing below the nut that connects the tubing to the component. The meter display should show that a thermocouple can reach close to 25 millivolts after it heats up; a thermopile should test between 350 millivolts and 900 millivolts after being heated. A thermocouple that tests well below 25 millivolts, or a thermopile that tests below 350 millivolts, will not be able to keep the pilot lit. If going through this testing process feels too daunting, consider this: if the spark electrode and the pilot itself appear to be in good condition, chances are the thermocouple or thermopile is the cause of the problem and the component will need to be replaced.
Gas Water Heater Pilot Not Lighting? Gas Water Heater Troubleshooting

Repair Clinic has genuine OEM water heater parts

When replacing a spark electrode, pilot, or thermocouple on a water heater, it’s important to use a genuine original manufacturer (OEM) replacement part. OEM parts are the only ones you can be certain will be compatible with your Rheem, A.O. Smith, Bradford White, Bryant, Carrier, Coleman, Honeywell, Lennox, or any other brand water heater. Fortunately, Repair Clinic makes it easy to find the exact OEM part you need for your repair. Enter the full model number of the water heater in the Repair Clinic search bar to see a list of OEM parts that are fully compatible with that model. You can then use the “Part Category” (“Sensor & Thermistor”) and “Part Title” (“Thermocouple”) navigation filters to identify the specific component you need.

Free water heater repair content courtesy of Repair Clinic

In addition to providing you with genuine original manufacturer parts, Repair Clinic has a library of free repair help content. Click on the “Videos & Articles” tab on our website and begin exploring. Among the thousands of “How To” videos, troubleshooting articles, and product schematics, you’ll find a step-by-step procedural video showing you the correct way to replace a thermocouple on an A.O. Smith gas water heater (model GCV40200) as well as a video showing how to install a complete pilot assembly on the same model. By offering genuine OEM parts shipped quickly, along with the know-how you need to complete the repair yourself, Repair Clinic is your repair partner when it comes to fixing heating and cooling units, major home appliances, and lawn and garden equipment.

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