Pilot taking a long time to ignite burner

Discussion in 'Water Heaters and Softeners' started by 4lane, Jun 11, 2018.

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  1. Jun 11, 2018 #1

    4lane

    4lane

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    I have a second home where I turn off the water heater each time I'm not there, and start it back up when there. It's an AO Smith, LP that is 3yrs old, but used 20 times a year. Previously, to start it up, I'd go to 'Pilot' press and hold, hit the igniter a couple times and the light would start blinking right away. Lately, I do the same thing but the light will not start blinking until after holding the 'Pilot' button in with pilot light lit, for many minutes. The pilot lights after a couple clicks of the igniter, but again, the light won't start blinking (signaling it's ready to light the burner) for several minutes.

    What is the issue here? Originally I thought thermopile, but the pilot lights quickly. Is it just warming slowly now?

    Thanks!
     
  2. Jun 11, 2018 #2

    jeffmattero76

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    My guess is that air is in the gas line. In the future, you may want to turn off the gas valve that supplies the water heater. That will limit the amount of air that can get in.
     
  3. Jun 12, 2018 #3

    4lane

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    You think it's air in the line and not an issue with the thermopile not warming as quickly as it should?
     
  4. Jun 12, 2018 #4

    jeffmattero76

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    I am referring to why it takes so long to light the pilot in the firstplace. You could remove the thermocouple (or thermopile, I don't know the difference), and the pilot would still light, as far as I know. The thermocouple is then heated by that lit pilot flame, which generates a very small current in the thermocouple, which opens the gas valve. Essentially, the thermocouples function is to tell the gas valve, "ok, the pilot is lit, so send in the gas".

    I am not a plumber by trade, but have done lots of plumbing in my rentals. What I have stated is my understanding of how it works.

    Turning off the gas valve on the pipe that supplies the water heater will, in my opinion, limit any air that gets into the system to the length of pipe between that valve and the pilot.

    To speed the process when re-lighting it, if you have a drip leg in the gas line, you can loosen the cap on the end of the drip leg until you smell gas. Only a small amount of gas goes through the pilot, but a large amount goes through the piping. Be sure to re-tighten and bubble that connection after you tighten it.
     
  5. Jun 12, 2018 #5

    jeffmattero76

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    I believe the function of the thermocouple is to keep the pilot lit, but it has no function in the actual lighting of the pilot.
     
  6. Jun 12, 2018 #6

    4lane

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    The pilot lights quickly. It's the time between when the pilot is lit, and the burner is ready to be ignited that takes a long time.

    This timing of when the burner can be lit is indicated when a light starts blinking on a panel. It takes a long time for that to start blinking AFTER the pilot has been lit.
     
  7. Jun 12, 2018 #7

    jeffmattero76

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    I misunderstood your original post. That sounds to me like it is a weak thermocouple. You can buy a new one for about $8 at the orange big box or plumbing supply house. They are simple to replace. Should take about 20 minutes.
     
  8. Jun 12, 2018 #8

    4lane

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    Right, but I think you mean thermopile. I don't believe newer water heaters with an electronic gas control have a thermocouple; only a thermopile.
     
  9. Jun 12, 2018 #9

    jeffmattero76

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    As I stated earlier, I don't know the difference between the two.
     
  10. Jun 14, 2018 at 12:40 PM #10

    jeffmattero76

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    Fmkehoe99 likes this.
  11. Jun 14, 2018 at 3:23 PM #11

    RenewDave

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    If you have and A.O. Smith enclosed combustion HWH, it’s not just changing the thermopile. That HWH requires the whole pilot assembly be changed. It’s not cheap either. That HWH needs to be serviced. It could also be that the thermopile is not close enough to the flame and cannot heat up quick enough. Thermopiles create a lot more energy than a traditional thermocouple and need a good flame right on it. You’ve got the gas, it’s within the burn chamber where you’re having an issue.
     
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  12. Jun 14, 2018 at 10:43 PM #12

    4lane

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    W
    Why would the entire pilot assembly need to be changed? Are you saying the issue is something other than the thermopile?
     
  13. Jun 15, 2018 at 4:25 AM #13

    RenewDave

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    No. But, with this water heater the pilot assembly is one piece that includes the thermopile and is sold that way. The overheat sensor is built in to it also. If you call A.O. smith and give them your serial number they will give you the assembly number. It’s not that hard to change out.
     
  14. Jun 17, 2018 at 2:04 PM #14

    TomFOhio

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    Also with this water heater being only 3 years old they will probably send you the parts for free under warranty as
    most of the residential water heaters have 6 years. Call AO Smith tech line and have the model and serial numbers
    ready.
     
  15. Jun 18, 2018 at 3:32 PM #15

    Fmkehoe99

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    Yikes ! A. O. Smith Thermopile only, $69.
    Sure a lot more than the old six dollar thermocoupler
     
  16. Jun 18, 2018 at 3:49 PM #16

    RenewDave

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    69 is a great deal!
     
  17. Jun 19, 2018 at 1:02 AM #17

    Illinois_plumber

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    welcome to the world of a plumber. Be glad it’s only $69 and you can maybe do it yourself with messing something else up. And maybe now you’ll understand how we feel when we go to a customers house and provide quality service as quick as possible and done correctly but get complaints that we “cost too much”. Nothing is cheap anymore. Deal with it
     
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  18. Jun 19, 2018 at 5:20 AM #18

    Mr_David

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    Just adding a note. mainly for Jeff
    The old thermocouple only had to energize a small electro magnetic valve ( Pilot Valve ) that is manually opened while you light the pilot and the electro magnetic valve remains open as long as the pilot flame is on and the thermocouple is producing enough juice. Approx. 18 millivolts.
    The Electronic control valve require more juice. Thermopiles make approx. 400 millivolts.
    Wall heaters that have a remote thermostat also use thermopiles to produce enough current to operate the state and open and close the main gas valve.
     
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  19. Jun 19, 2018 at 12:31 PM #19

    jeffmattero76

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    Mr. David - thanks! I appreciate the explanation and the education.
     

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