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Thread: AO Smith FPS 50 Powervent Water Heater: Burner won't stay lit, blower keeps running

  1. #1
    DIY Junior Member SWittmier's Avatar
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    Default AO Smith FPS 50 Powervent Water Heater: Burner won't stay lit, blower keeps running

    I have an AO Smith FPS 50 226 Powershot gas water heater. When there is a demand for hot water, everything starts up normally, but the burner goes out (can hear the solenoid click shutting it down) before the water is up to temp (the blower continues to run and the pilot is lit). While the blower is running, the burner may refire at some point, but then it shuts down again. If I reset it using the on/off switch on the blower, it will refire and continue to burn until it shuts off properly, though not always the first time. I've run some of the tests outlined by the tech manual, but it doesn't seem that this condition fits the ones covered. The blower, power cable (tested for 120 at both and got it), and gas valve solenoid are all fine (replaced the latter to no effect). The wire harness that connects the power cable to the gas pressure valve and solenoid is not showing 120 volts (in fact it shows 0) to the solenoid (according to the manual this could indicate that the harness needs replacement), but continuity is good in all 4 wires (no shorts). Haven't tested the gas valve for pressure yet, nor have I tested the gas pressure switch (though the conditions according to the manual don't point to this being a problem, and I'm not sure how to do that specifically even if it did). I know the water heater is old (about 12 years), but I'm not in a position to replace at the moment. Could it still be the harness, the gas pressure switch, or is there something else I should be looking for?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Is there a flame detector in the thing? IF so, it may not always be detecting that the flame is on, and then it will shut down, usually go into a purge cycle (keep the fan on), then try to relight, assuming it is still calling for heat.
    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 SWittmier's Avatar
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    Not sure about the flame detector. I've been through the parts diagram and have seen nothing of the sort. Haven't pulled anything out from underneath yet (Pilot tube, thermocouple, etc.) to check, though. I've read that flame sensors can be a problem, just not sure if mine has one. Will be poking around here shortly.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    May not be a flame sensor (other than that heated by the pilot). There may also be a pressure sensor that isn't working, but that often would prevent the flame from even starting to come on. Depends on where it is in the safety circuits. If the exhaust is partially plugged, that can affect things enough so that the pressure sensor won't allow the flame. these are generic comments, and may not apply to that device. If you read the theory of operation in the manual, and can follow the block diagram, it should help point you to the problem.
    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 SWittmier's Avatar
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    O friggin' MG. So, get this: I was at Home depot today picking up a gas test gauge to test the main gas valve (wanted to do it anyway, just to be sure). I was explaining to one of the associates what was going on and a gentleman overheard our conversation. Turns out the guy does nothing but water heaters and told me that probably 80 to 90% of the time when there's a problem like mine, it's that the blower is so caked full of dust that the fan can't move enough air to let the air pressure gauge to it's job right - the gauge thinks there's not enough air moving so it sends out a signal to shut off the burner. All right, so I went home, dismantled the blower and cleaned it all out. After hooking it all up, I triggered the thermo to call for heat. Everything started up normally, and lo and behold, after waiting for about 5 minutes, the burner shut off, and in a couple of seconds, so did the burner!!!! Wow! Anyway, gonna keep my eye on the whole thing, but if that was the problem, pass the word and maybe we can save some people out there a load of money. I'll post updates if anything changes. Thanks for the input Jim!

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    DIY Junior Member Jarcher's Avatar
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    I have a A.O. Smith Power shot water heater. It is a 50 gal. I have had the same problem. It won't stay lit. I was getting a system lock out code. I tested every option under system lock out . the green light on and A & B on. I read about 100 blogs with people getting the same problem without sucess. I called A.O 's techs 3 times and they said it had to be in those areas. I finally decided to check the blower unit even though A.O's techs said it wouldn't be. Before I did, I checked the vaccuum switch on the side of the blower. It is a small black disc about the size of silver dollar with a clear plastic tube running to it. I blew in it and turned the start switch on. As long as I blew and kept pressure on the switch , the flame would not go out and soon as I stopped blowing in the tube,it went out.That hose has to have consent air pressure so it knows the the fan is moving exhaust from the flame or it shut the gas valve off. It is a quick way to check with out pulling the blower. the other end of the hose that you disconnected from the barbed brass fitting. You can blow through the brass barbed fitting. You should find it plugged. You can clean it with a pipe cleaner if you don't want to pull the blower assembly. Mine has been running great since I cleaned that brass fitting going to the hose that goes to the vaccuum switch. Hope this helps. John in
    Davison,Mi.

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    DIY Junior Member reasonerj's Avatar
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    I have a A.O. Smith Power-shot water heater. It heats fine when it needs to but the power vent runs all the time. Why?

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    DIY Junior Member billydgb's Avatar
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    Default AO Smith FPS 50 226 - not working, please help

    Most of what I know about water heaters is from the research I've done in the last 24 hours, so first of all i'm a total novice.

    The water heater is 19 years old... given its age, the time of year and the fact that we're gonna have a dozen people here for Xmas I almost had a guy come out here today to replace it for a mere $1,800 (sorry kids, hope you enjoyed your shower). Anyway, I live in Minnesota and it has been crazy cold (if that affects anything at all, like -30). I have smelled trace amounts of natural gas lately so I shut off the gas valve last night... today, I turned it back on and lit the pilot, it stayed on, but after turning the knob to ON, setting the water temp to "A" (I assume means "average") and flipping the breaker back on, the burner did not light, the blower didn't do anything (I tested the outlet so it's getting power). A friend of mine said paying $1800 is just stupid and its probably a $10 thermocouple - another thread on this site claims the blower was clogged with dust was preventing enough air flow to initiate it working. I pulled the little air tube from one side and couldn't blow any consistent air through it, but while inhaling i could hear a switch of some kind - i tried the other way and couldn't blow or inhale much. I understand there are about 7 things that have to happen in order or it won't light the burner. Every plumber in town is crazy busy and may take several days to come out (unless they hear you have a check for $1800 then they'll be out in 15 minutes, ugh). I checked the exhaust tube on the side of the house, with the exception of a little icicle hanging off the bottom lip of it, it wasn't clogged. I don't know what to do other than maybe order a thermocouple. The blower is a 3000 RPM Ametek. Any advice would be so appreciated. I'm attaching a link to a short video of the burner area, not sure if it shows anything - kinda looks like a layer of crap needs to be cleaned off of it? please, help me save xmas...

    http://www.youtube.com/watch?v=MmhEC...ature=youtu.be


    http://www.hotwater.com/lit/training/tc034.pdf
    Last edited by Terry; 12-11-2013 at 11:00 PM. Reason: added link

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    Retired Defense Industry Engineer jadnashua's Avatar
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    That click was probably a vacuum switch. IF the air isn't moving properly, the fan cannot create a suction, indicating that either the intake or outlet is block (depending on where the sensor is). When it is flowing properly, it can pull a vacuum, which is likely in the interlock circuitry.
    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 billydgb's Avatar
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    I have a working water heater again!! It didn't register in my brain that a week ago I changed positions of a lever on my furnace from one extreme to the other (located close to the ceiling above the furnace), I was told to do this to see if the "new addition" side of the house would stay warmer (the addition was built 10 years ago) - there is an air duct that runs over that way and it was slightly warmer for a few days. I woke up last night remembering this change I made, this morning I switched the lever back to where it had been positioned for years and also vacuumed a ton of soot off the top of the burner, lit the pilot - it started up and has been working like a charm all day. However, I now have to convince other people living here that the $1800 replacement may not be needed, it's scheduled for Monday morning - I can't win - now the concern is maybe this heater is unreliable and will fail around Christmas. Is it possible that doing essentially a "switch track" on my furnace caused inadequate air flow and caused the water heater to fail? Or is the exhaust off the water heater entirely separate? Maybe cleaning the soot off the burner did the trick...? All I know is that the damn thing is working and I don't wanna be the guy that ruined Christmas... like I said, I can't win. Your comments are very appreciated...

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    Retired Defense Industry Engineer jadnashua's Avatar
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    If you did anything that created a restriction in the flue, the power vent system in the WH would shut it down. If you disrupted the airflow into the area of the combustion devices, somehow restricting incoming air (or depressurizing it by blowing an extra amount out), you might shut down the WH. All combustion devices have certain requirements about their air movement, and often have safety circuits installed to protect against problems (which is probably why it would not light). So, it may no longer be an issue. If you could demonstrate flipping that vent back to where it was shut the thing down, and that when it's back where it should(?) be it works, that may be enough to quell distrust of the thing, but nothing is certain...any mechanical thing eventually wears out, and it could be its time.
    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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