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gas control problem on ao smith water heater

zepfan Member Posts: 398
i am having an issue with a AO smith water heater model# fcv 40 100.installed in 2004.The pilot is lit, and the heater is online, and not leaking.The millivolt signal from the thermocouple is 28 mv.The problem is that about every 10-15 minutes the main burner goes off,and the pilot goes out.The inlet gas pressure appears to be ok,the furnace that is next to it has had no issues.I don't know what else this can be other then to replace the gas control.Does anyone know that on this model does the entire heater have to be drained to replace the control? I would guess yes.Thanks to all


  • Snowmelt
    Snowmelt Member Posts: 1,416
    Y es, it. Does ao smith seems to have problems with gas valves. It's only 40 gallons.
  • Robert O'Connor_12
    Robert O'Connor_12 Member Posts: 728
    Yes, you must drain first to replace gas valve. Many times it's the FVIR screen. Have you checked and cleaned it? Blow it out with air, or vacuum it real good.
  • Rich_49
    Rich_49 Member Posts: 2,766
    Robert is correct . Before anything else clean the screens around the bottom exterior and the one under the tank . I'm betting this will solve your issue .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Don_197
    Don_197 Member Posts: 184
    If you can get a look at it when it is going out........this is a good test. If it drops like a rock.......one second its on....the next its off.....its probably the valve. If it "ghosts" out........in other words the flame starts to wave and look "ghosty" and then goes out.....its a lack of combustion air (or in rare cases.....recirc of the exhaust back into the intake) then your screens are pluggered.
  • Steam_Starter
    Steam_Starter Member Posts: 109
    I was having the exact same problem with my FVIR water heater. see below earlier post from me:

    "FVIR- Ugh.

    I was having the same exact problem. PL would go out when it wanted to (but usually before the first AM shower.) I pulled the burner assembly and vacuumed the inside of the burner box. Paid close attention to the FVIR stamped intake screen in the bottom of the unit. Blew it out and it was full of dust and cat dander.) Gave a good vacuum under and around the unit and it has been working fine ever since (about 3 months ago.)

    Sometimes you need to reverse flow the shop vac and blow into the screen then vacuum underneath. The intakes are way too small and any dust that accumulates on the screen starves the unit and POOF. Pilot goes out."

    Good luck with it.
    "Hey, it looks good on you though..."
  • zepfan
    zepfan Member Posts: 398
    thanks to everyone for posting, i cleaned out the screens and installed an air filter that wraps around the bottom of the heater. so far, so good
    Robert O'Connor_12