Announcement

Collapse
No announcement yet.

Effect of excessively large pilot light.

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Effect of excessively large pilot light.

    Tonight I had to replace a thermocouple on a boiler as the old thermocouple failed. After replacing the thermocouple and lighting the pilot I observed it was an unusually large pilot. The thermocouple glowing a dull red. I pointed this out to the owner, and offered to get a smaller pilot orifice on Monday.

    Then since the owner didn't know how to light their pilot light so I decided to show them. That's when I learned something myself. I turned the gas valve to "off" so the pilot shut down. Then I showed them how the gas valve knob couldn't be depressed in either the "off" or "on" position. However, once I turned the gas valve to the "on" position even though I couldn't depress the button the gas poured into the combustion chamber!! This was perhaps 10 seconds after I had shutoff the pilot light. I turned the gas valve to the "off" position, and then back "on" and gas poured into the combustion chamber again. I repeated the process again with the same result.

    Perhaps thirty seconds later I heard a click. I turned the gas valve to "on". No gas entered the combustion chamber. The click was the pilot solenoid valve finally shutting. I suspect that even without the pilot light operating thermocouple was so hot it kept producing sufficient voltage to keep the solenoid energized for nearly a minute after the pilot was out.

    This situation can permit the development of a potentially catastrophically explosive situation. If the pilot light were extinguished for any reason, and the thermostat called for heat anytime within the next 45 seconds the main gas valve can open and allow gas into the combustion chamber without a controlled ignition source. Bad juju!

    So large pilot lights can be a safety hazard in addition to costing more $$ to operate.
    Time flies like an arrow.

    Fruit flies like a banana.

  • #2
    Re: Effect of excessively large pilot light.

    The quick answer is yes. A thermocouple will hold the gas valve pilot open for up to 45 seconds while an intermittent spark valve will only hold it open for 8/10 ths of a second.

    Comment


    • #3
      Re: Effect of excessively large pilot light.

      The thermocouple was working fine. even at a normal pilot level the thermocouple should hold the gas valve open for at least 30 seconds after the pilot is exstinguished.

      Comment


      • #4
        Re: Effect of excessively large pilot light.

        Originally posted by saysflushable View Post
        The thermocouple was working fine. even at a normal pilot level the thermocouple should hold the gas valve open for at least 30 seconds after the pilot is exstinguished.

        Myakka and Says: This is interesting news. I always thought the pilot going out should prevent main gas flowing within a few seconds. I once tested a new water heater I installed (maybe 10-15 years ago) by snuffing the pilot light while the heater main burner was operating and the gas shutoff within a second or so. It was pretty much immediate. I'll check this on my water heater to see what happens and post it. Although I presume how long it stays lit is a function of how much voltage the thermocouple puts out vs what's required to energize the solenoid coil.


        BTW: The customer mentioned that the thermocouple on this boiler fails every three years or so.
        Time flies like an arrow.

        Fruit flies like a banana.

        Comment


        • #5
          Re: Effect of excessively large pilot light.

          Almost every gas valve on a boiler will have a pilot adjustment. I would dial it down first before changing the pilot orifice. I've found that on older ones, the pilot flame adjusts very little no matter which way I turn the screw. An overheated thermocouple will fail more often but every three years is not unheard of.

          Comment


          • #6
            Re: Effect of excessively large pilot light.

            It's the only very inconclusive test you can do to a gas valve to determine if it is bad. 1st make sure the thermocoupler is putting out proper voltage. then attach thermocouple and heat it up in the pilot light for a while. extinguish pilot and time how long before you hear the click. it should be at least 30 seconds. if it clicks under 30 the gas valve is bad if it clicks after30 the gas valve might still be bad.

            Comment


            • #7
              Re: Effect of excessively large pilot light.

              Neat way to test a thermocouple.....

              Find old water heaters, remove the thermocouple from the gas valve and then remove the magnet assembly from the gas valve.

              To test a thermocouple, remove the suspect thermocouple from the valve and burner. Screw it into the magnet. Light a propane torch on low flame, hold the magnet closed simultaneously heating the tip of the thermocouple, wait about 45 seconds then release the pressure on magnet. If it holds...good thermocouple.
              AllurePlumbing.com
              • leak detection
              • drain cleaning
              • utility locating
              • conductor fault locating
              • and other specialties.

              Greensboro NC, Winston-Salem NC, High Point NC, Thomasville NC, Kernersville NC

              Comment


              • #8
                Re: Effect of excessively large pilot light.

                Originally posted by saysflushable View Post
                It's the only very inconclusive test you can do to a gas valve to determine if it is bad. 1st make sure the thermocoupler is putting out proper voltage. then attach thermocouple and heat it up in the pilot light for a while. extinguish pilot and time how long before you hear the click. it should be at least 30 seconds. if it clicks under 30 the gas valve is bad if it clicks after30 the gas valve might still be bad.

                Says: I just finished checking my water heater to see how long before the solenoid closed after the pilot was extinguished and it was just about 30 seconds. I also turned the gas valve on to see if it would let gas into the combustion chamber and it did. I also turned up the thermostat in this time frame and the gas valve let gas into the combustion chamber.

                Now I'm wondering who had that water heater I checked waaaay back when. )
                Time flies like an arrow.

                Fruit flies like a banana.

                Comment


                • #9
                  Re: Effect of excessively large pilot light.

                  I went back to the customer's house for a different job. I shut off the pilot and used the stopwatch on my phone to measure how long it took for the solenoid to de energize. One minute five seconds. When I replace the pilot assembly to get a smaller flame I'll check the time again and post it here.
                  Time flies like an arrow.

                  Fruit flies like a banana.

                  Comment


                  • #10
                    Re: Effect of excessively large pilot light.

                    I replaced the pilot assembly today. The first pilot light was 2-1/2 - 3" long although it's hard to see in the image.

                    The new pilot is considerably shorter and doesn't heat up the thermocouple to the point that it's bright red.

                    When the original pilot was extinguished it was 65 seconds till the solenoid de-energized.
                    When the new pilot was extinguished it was 23 seconds till the solenoid de-energized.

                    I started and stopped the main gas valve multiple times and the new pilot never faltered.

                    The homeowner will save energy, and shouldn't be installing thermocouples every three years.
                    Attached Files
                    Time flies like an arrow.

                    Fruit flies like a banana.

                    Comment


                    • #11
                      Re: Effect of excessively large pilot light.

                      Sounds like someone else tried cleaning it and lost the orifice or made it bigger by trying to clean it.
                      AllurePlumbing.com
                      • leak detection
                      • drain cleaning
                      • utility locating
                      • conductor fault locating
                      • and other specialties.

                      Greensboro NC, Winston-Salem NC, High Point NC, Thomasville NC, Kernersville NC

                      Comment


                      • #12
                        Re: Effect of excessively large pilot light.

                        Originally posted by Gettinit View Post
                        Sounds like someone else tried cleaning it and lost the orifice or made it bigger by trying to clean it.
                        You know that is EXACTLY what I thought except the orifice was there and looked perfect.
                        Time flies like an arrow.

                        Fruit flies like a banana.

                        Comment

                        Working...
                        X