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AO Smith TCO Switch Part#

djpetramw Member Posts: 1
I have searched high and low for this part number! 😡 I have an A.O. Smith hot water tank, model GCV-40 200. I need the part number for the TCO (thermal cutoff) switch. I would be eternally grateful if someone could help.


  • I don't think it has one. The temperature and pressure relief valve will serve this function on residential models.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,247
    edited June 2022
    Hi @djpetramw , Looking through the manual, I see a part called "thermocouple TCO" , which I'm guessing means thermal cut out. If so, the thermocouple assembly contains a thermal cut out and you need to order the whole assembly to get that part, which is integral with the thermocouple. :|

    I should add that the ECO probably failed for a reason. It's there to help prevent overheating in the combustion chamber. If the air inlet screen gets dirty, it can reduce airflow into the chamber and allow it to heat up more than normal. So clean the screen under running water before firing up the heater again with it's new thermocouple assembly, or the new one might live a short, unhappy life. >:)

    Yours, Larry
    Alan (California Radiant) Forbes