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100 gal ao smith water heater mistery

ph Member Posts: 11
i got a no hot water call on a 16 yr old ao smith 100 gal 75k btu's i replaced the thermocoupling and tightened the pilot tubing all worked fine for 2 weeks, then i get a call no hot water again so i come and find that the thermocoupling is all burnt up so i replace the pilot tubing and the thermocoupilng thinking the tubing got over heated and is not holding good, it works for 2 weeks then i get a call no hot water so i go down and its burnt again so i decide to clean the heater thinking it durty and its making the flame ti hot losing the tubing and burning up the thermocopling, 2 weeks go by its out again, i replaced the pilot, pilot tubing and thermocoupling , waiting to see whats going to happen in 2 weeks any ideas on what to look for if it dose?


  • kcopp
    kcopp Member Posts: 4,443
    Where is....

    the water heater? is there some type of bleach or salt in the area? Is the gas pressure too high? Natural or LP?
  • ph
    ph Member Posts: 11
    high gas pressure

    the only thing that changed that i remembered after i left is that the gas company put high gas pressure in this summer.. so if it comes back in i will run the water heater and turn on all the other heating units to see if it dips out... any other suggestions?
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    the gas company put high gas pressure in this summer..

    Where I live, the gas mains in the street were nominally 15 psi, though when they metered it, it was about 8 psi. This in the summertime. This summer they replaced the old iron pipe with about 4 1/2 inch or 5 inch plastic pipe down the main street, and kept the 3 inch plastic pipe that runs from the mains down my street. It is supposed to be 50 psi, and that is what the meter said.

    They said my meter and regulator could deal with the higher pressure and I would have less problems in the wintertime. Well, I did not have problems in the winter time. They checked every house pressure after the regulators, and presumably they were all about 7 inches; mine was 7 inches just as before. The meter should not be affected since it comes after the regulator.

    But if your regulator was old, perhaps it could not manage the new supply pressure and is putting out to high a pressure. Gas company should be able to measure it for you.
  • Tim Schram_2
    Tim Schram_2 Member Posts: 17
    Just to be sure..

    I would definitely use a manometer to check INCOMING gas pressure to the gas control valve which should be about 7 inches of water column with probably a 3.5 inch manifold pressure going to the burner.  If the incoming is too high you may need to add a regulator at the unit to bring it down to 7inches then recheck the manifold pressure.  If incoming is good (check it with the unit running) then the internal gas control valve regulator is the most likely culprit.

    Hope this helps
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