Water Heater Pilot Light Won’t Stay Lit After Thermocouple Replacement

Replacing the thermocouple is often the first solution when the pilot light won’t stay lit. But in several cases, this solution is not enough. 

In order for a thermocouple to work properly, it needs to be installed correctly. Other parts of the water heater need to be in top shape, too. For instance, there shouldn’t be excess debris or water outside of the tank.

Sometimes, the pilot light won’t turn on because your new thermocouple is faulty or installed incorrectly. Other times, there may be debris in the pilot tube, water in the gas pipes, or a malfunctioning temperature control valve.

This article will explore the reasons for these issues and how to fix them.

Reasons Why Your Pilot Light With a New Thermocouple Won’t Stay Lit

Here are a few reasons why the pilot light won’t switch on despite replacing the thermocouple:

pilot light thermocouple issue

Thermocouple Is In the Wrong Position

Be sure to insert the thermocouple into the holder more deeply. You should ensure the pilot flame engulfs ⅜ inch of the tip of the new thermocouple. Thermocouples need heat from the pilot flame to keep the gas valve open. 

Debris in the Pilot Tube

Dirt, dust, and debris can block gas flow in a pilot tube, preventing your pilot light from getting the fuel it needs to ignite. This issue occurs more often in old water heaters. 

Water in the Gas Pipes

Low-pressure gas systems are susceptible to condensation of water vapor. In simple terms, water vapor from the heated components seeps into the gas pipes and condenses, thus reducing the flow of gas through the lines. 

This should be on your list of suspects if you’re using a low-pressure gas system. Call a technician to verify the problem. 

Malfunctioning Temperature Control Valve

The temperature control valve maintains the internal temperature of the water heater and shuts off when the internal temp gets too high. In most cases, a faulty control valve will also shut off the gas supply to the pilot light. 

Faulty Thermocouple

Sometimes, the pilot light will not stay lit if the new thermocouple is defective. The thermocouple controls the opening and closing of gas valves. So if a thermocouple is faulty, it can’t keep the gas valves open correctly. This interferes with fuel flow to the pilot light.

How Do I Know if the Thermocouple is Defective? 

Pilot flames heat a thermocouple, producing enough current to keep the gas valves open. If the pilot light went out once you released the gas control knob, you probably have a defective thermocouple.

You can also test the voltage levels of your thermocouple to determine if it’s faulty. A reading that’s too low indicates a malfunctioning thermocouple. Refer to the below instructions for how to check voltage levels:

pilot light water heater not lit

How to Read Voltage Levels

First, ensure to turn off the gas reserve and ventilate any strong gas odors if you’re working with a gas-powered water heater. Then follow these steps:

  1. Get alligator clip test leads, an adjustable wrench, and a multimeter. 
  2. Open the cover at the base of the water heater. Secure all electrical connections.
  3. Using an adjustable wrench, remove the thermocouple from the control valve. 
  4. Bring out the multimeter and switch it to the voltage settings. 
  5. Connect alligator clip tests to the multimeter. Clamp one alligator clip to the copper tube of the thermocouple and another to its end. 
  6. For electricity-powered gas heaters, light the pilot by pressing and holding down the button that opens the gas valve. The voltage should increase as the thermocouple gets hotter. 

A healthy thermocouple should have a voltage reading between 20 to 30 millivolts. If the thermocouple passes this test, check the air vents for debris.

Solutions for Pilot Light That Won’t Stay Lit After Replacing Thermocouple 

Once you have identified the cause of your pilot light not staying lit, consult the steps in the sections below:

How to Remove Dirt from Pilot Tubes in a Water Heater 

  1. Insert a needle or office pin into the pilot tube. You’ll feel resistance at first, but keep pushing.
  2. Push the needle in and out of the tune until there’s no resistance. 
  3. Blow air to remove remaining debris. 

How to Replace a Damaged Thermocouple in a Water Heater 

  1. Use an adjustable wrench to loosen the nut connecting the thermocouple to the control valve and remove the gas line from the pilot line. 
  2. Pull out the thermocouple with the whole burner assembly.
  3. Gently pull the thermocouple out from the burner assembly. 
  4. Push a new thermocouple into the slot. If there’s a screw to hold it in place, tighten it.
  5. Reattach it to the control valve and the gas line to the pilot light. 

Note: Go for a universal thermocouple if you can’t get the thermocouple specific to your water heater. 

How to Replace a Faulty Control Valve 

Replacing a faulty control valve is a delicate process. You may need the assistance of a licensed repairer. If you insist on doing it yourself, follow the below steps: 

  1. Switch off the gas valve and drain the water heater.
  2. Remove the control valve.
  3. Unscrew the burner assembly. Use an adjustable wrench to remove the thermocouple from the control valve and unscrew the gas line from the pilot light. 
  4. Remove the burner assembly. 
  5. Take a half-inch nipple and thread it into the gas control valve. Screw the nipple tightly and use it to rotate the gas control valve in an anti-clockwise direction. 
  6. Remove the valve and add in a replacement. 
  7. After installing the control valve, reattach the thermocouple and burn assembly. Ensure there’s no loose joint or screw before switching on the gas supply. 


Hopefully, these fixes have solved your pilot light pickle. Consult with a professional if you have tried cleaning the pilot tubes, draining water, and replacing the faulty control valve or thermocouple and your pilot light still won’t stay lit.