How to Troubleshoot a Gas Water Heater With No Hot Water

Female electrician checking boiler


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If your gas hot water heater isn't making any hot water, chances are the pilot light is out. As a result, the burner that heats the water never turns on. Pilot lights can go out when there's nothing wrong with the appliance. In this case, all you have to do is relight the pilot and the problem is solved. However, if you relight the pilot and it doesn't stay on, you likely have a bad thermocouple. Otherwise, you could have problems with the gas control valve.

Lighting a Gas Water Heater Pilot Light

Gas water heaters have two different types of pilot lights. The older style requires manual lighting with a match or a barbecue lighter. The newer style uses a spark igniter (Piezo igniter) that you activate by pushing a button, which creates a spark to light the pilot. The basic steps for lighting either type are similar, but always follow the lighting instructions posted on your water heater.

  1. Turn the pilot control knob on the water heater to OFF.
  2. Wait 10 minutes to ensure the burner compartment is cool and to allow any gas from the pilot to dissipate.
  3. Turn the pilot control knob to LIGHT.
  4. Light a match or prepare a barbecue lighter (for manual-light pilots only).
  5. Press down the pilot knob all the way, and hold it down. Immediately reach in with the match or barbecue lighter and light the pilot. If you have a spark igniter, press the igniter button (it's usually a red button next to the pilot knob) to create a spark.
  6. Confirm that the pilot flame is burning while keeping the pilot knob pressed. Hold the knob down for 30 to 60 seconds.
  7. Release the pilot knob so it pops back up, then turn the knob to ON.
  8. Confirm that the pilot is still on. If it has gone out, repeat the same process one or two times. If the pilot still won't stay on, consider replacing the thermocouple.

Replacing a Thermocouple

Replacing a thermocouple is a fairly easy job with an older-style manual pilot light. If you have a spark igniter pilot, call a plumber for the repair; heaters with this type of pilot have a sealed burner compartment and are more complicated to work with.

The thermocouple is a sensor that tells the gas valve to allow gas to flow to the burner. One end of the thermocouple is attached to the gas valve; the other end is positioned to be in the pilot flame. A copper wire connects the ends of the thermocouple. Heat from the pilot flame creates a small electrical charge that tells the gas valve that the pilot is going. If the pilot is out, the gas valve stays closed.

  1. Turn off the gas supply to the water heater at the shutoff valve on the gas pipe leading to the gas control valve. On the control valve, turn the pilot control knob to the OFF position. 
  2. Make sure the burner area of the water heater is cool; if not, allow it to cool completely.
  3. Remove the access panel of the burner assembly. There may be an outer and an inner cover.
  4. Locate the thermocouple connection at the bottom of the gas control valve. Look for a copper wire going into a hex nut at the control valve housing.
  5. Loosen the nut connecting the thermocouple to the control valve, using an adjustable wrench. Pull the nut and thermocouple wire away from the valve housing.
  6. Reach into the burner compartment and carefully twist the thermocouple from its bracket to loosen it.
  7. Pull the thermocouple out of the bracket, being careful not to bend the bracket; the thermocouple should come out easily once it's loose. Remove the thermocouple from the burner compartment.
  8. Bring the thermocouple (with the hex nut) to the hardware store, home center, or plumbing supply store and buy an exact replacement.
  9. Straighten the wire on the new thermocouple, then bend it similarly to the original; it doesn't have to be precise.
  10. Insert the new thermocouple into the burner assembly, and twist and push it into its bracket, as with the original.
  11. Position the thermocouple tip so that the pilot flame will envelop the top 3/8 to 1/2 inch of the thermocouple tip.
  12. Connect the outer end of the thermocouple to the gas control valve, using the hex nut. Make sure the nut is not cross-threaded, and tighten it by hand. Then, tighten the nut about one-quarter turn with the wrench. If the thermocouple wire feels loose, tighten the nut a bit more, but be careful not to over-tighten.
  13. Reinstall the burner access cover(s).
  14. Open the gas shutoff valve.
  15. Light the pilot light following the manufacturer's instructions.
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 The Spruce, 2018