Reply With QuoteIs 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.
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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?
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
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.
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
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!
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.
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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