How to Fix a Water Heater Pilot Light

Replacing the thermocouple usually does the trick.

Next Project
Time

An hour or less

Complexity

Beginner

Cost

Less than $20

Introduction

If your hot water heater suddenly stops working, chances are a bad thermocouple has shut off the gas to the pilot light. Replacement is an easy DIY repair.

Tools Required

  • 4-in-1 screwdriver
  • Adjustable wrench
  • Wrench set

Materials Required

  • Dish soap
  • Long matches
  • Thermocouple

No hot water? If you have a natural or propane gas water heater, chances are the pilot has gone out. The water heater pilot light is a small flame that ignites the gas burner on your water heater. When the water heater pilot light goes out, first try relighting it, following the directions on the water heater label. If the pilot doesn’t relight, if it goes out right after lighting or if it goes out repeatedly, by far the most common cause is a bad thermocouple. The good news: You can usually replace a thermocouple for minimal cost and in less than an hour. You’ll get your hot water going without waiting for a professional to show up and you’ll save the cost of a service call.

Read on to learn how to light a pilot light.

What is a Thermocouple?

  • A thermocouple senses the heat of the pilot and allows gas to flow to the burner.
  • A bad thermocouple will shut off gas to both the pilot and the burner so the pilot light won’t stay lit.

Project step-by-step (6)

Step 1

Turn Off the Shutoff Valve

  • Turn off the shutoff valve to the gas line.
  • Be sure to turn the valve one-quarter turn so that the handle is at a right angle to the pipe, as in this photo.

Step 2

Unscrew the Nuts

  • Turn off the control valve.
  • Remove the burner access covers and unscrew the nuts on the gas, pilot and thermocouple lines.

Step 3

Remove the Assembly

  • Pull out the water heater pilot light burner assembly.
  • Unscrew or pull out the old thermocouple.
  • Buy a new one that matches the old one in size and length.

Step 4

Install the New Thermocouple

  • Install the new thermocouple exactly like the old one.
  • Slide the burner assembly back in.
  • Reattach the three lines to the control valve.

Step 5

Reattach the Lines to the Gas Valve

  • To reattach the three lines to the gas valve, thread the nuts into place with your fingers and hand-tighten them.
  • Snug them up with a quarter to half revolution with a wrench.
    • Pro tip: The metals are soft, so don't overtighten.

Step 6

Test for Gas Leaks

    • Note: You must have the pilot lit and the burner on to test for leaks, so that gas is flowing through the large tube.
  • Reopen the shutoff valve.
  • Relight the pilot light.
  • Turn the control valve to “on”.
  • When the gas burner comes on, use a 50/50 dish soap/water mix to test the screw joints for air bubbles that indicate leaks.
    • Note: When relit, the water heater pilot light flame should wrap around the thermocouple bulb.

CAUTION!

You should not be able to smell gas during this operation (except for a slight whiff when you remove the gas lines). If you do, leave the house and call your gas utility.

When Not to Replace the Thermocouple

Some gas water heaters have a “closed” burner chamber, which is difficult to access. We recommend that you call a service pro to fix this type of heater. Also, some gas water heaters don't have pilots. Let the pros fix these as well.

Closed burner chamber

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