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Thread: A.O. Smith GPDH 50 100 - Pressure switch error

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    DIY Junior Member Janky's Avatar
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    Default A.O. Smith GPDH 50 100 - Pressure switch error

    I have searched as much as I can around this forum for ideas and even found some manuals on how to test the pressure switch. I am just looking for any thoughts on this and also if someone could tell me where the switch is. Here is what I have collected this far.
    A.O Smith "type"


    Tag on side of water heater


    Error Code:


    Manual's description of error code:

  2. #2
    DIY Junior Member Janky's Avatar
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    Here are a couple shots of the unit

    Are those wires in the center connected to the pressure switch? I would guess that is it, or at least some kind of switch (2 wires)


    That clear air line looks like a vacum line to me, but I don't know. Either way, if I pull that while it is running, I can produce the same error code. (?)

    Also, after the unit shuts itself down with the error code, I can unplug it then replug it in, and it will run great (until it fails again which seems to be "random")

    The hoses going outside the house seem fine.

    The water heater ones are the two on the right


    The inlet is on the far right with the valve

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    DIY Junior Member Janky's Avatar
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    The outlet looks clear, but I cant see all the way down.


    Thoughts? Thanks!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    I'd agree, the hose is the vacuum line and it must connect to the switch somewhere. If there are any leaks (hose split, bad connection, etc) , the fan doesn't run at the proper speed, there's an obstruction, there's a crack or bad connection in one of the pipes, or possibly, the pipes are too long (effective which gets compensated by both the length and the elbows) - any of those can restrict air flow by the vacuum (pressure) switch. Course, the switch itself could be bad, or there's a loose connection to it or even the circuit board isn't responding properly to the input.

    As you can see, there's a lot of possibilities. First thing I'd consider is looking closely at everything for a leak, either into or out of the pipes.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Plumber jimbo's Avatar
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    That tube is not vacuum, it is the pressure sender and whatever it connects to on the other end, that is the switch. Replace the switch and tube, but also check the fitting on the blower end for obstruction

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    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by jimbo View Post
    That tube is not vacuum, it is the pressure sender and whatever it connects to on the other end, that is the switch. Replace the switch and tube, but also check the fitting on the blower end for obstruction
    Agreed, that fitting and the hose appear to be connected to the discharge side of the blower, not the suction side.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Whether vacuum or pressure, the idea is the same...if there's a leak or obstruction, or the fan isn't running properly, the pressure/vacuum can get out of tolerance and the switch won't operate. The switch itself could be bad or the electrical connection to it, or any of the other things I originally mentioned.

    Had an old boiler with a concentric pipe for closed combustion and one of the internal elbows cracked...the switch shut the system down. Don't remember if it was a vacuum or pressure switch in that case, but the sensor can go on either side, depending on your design. Since it is more corrosive on the exhaust (pressure) side, I'd rather not see it there, but if it is the pressurized supply air, that's not an issue. In that case, there was a recall, and they replaced the pipe under (extended) warranty.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member Janky's Avatar
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    Quote Originally Posted by jimbo View Post
    That tube is not vacuum, it is the pressure sender and whatever it connects to on the other end, that is the switch. Replace the switch and tube, but also check the fitting on the blower end for obstruction
    Well, I finally got a new pressure switch, and replaced it last night. Woke up this morning with the water heater showing the same error. Tonight I will pull that hose out and test it for cracks. I guess I can cut that "seal" made on the blower side PVC and lift it off the blower to look for junk built up in it.

    If these two don't solve the problem I am not sure what to do. I may just call a plumber over or something.

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