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Old 09-24-2017, 02:49 PM   #1
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Cannot light the water heater pilot light


I have an AO Smith FVR40100 Promax (aka The Water Heater from Hell). I cannot light the pilot light. I have tried the following : replaced the entire burner assembly including thermocouple, cleaned the pizo igniter with sandpaper, cleaned the ceramic disc in the bottom with brush, vacuum, and blew air thru it from top to bottom with an air compressor, checked the air flow up thru the vent to confirm it's strong enough, vacuumed the inside of the combustion chamber, confirmed I can smell gas when the black knob is pushed and held down, confirmed thermocouple, igniter and gas tube ends are approx 1/8" apart and end of thermocouple is in the flame, held down the black knob for a minute before trying to light, confirmed igniter produces a spark, had a plumber look at it who said he has no idea what the problem is (and then gave me a bill for $177). What else can I try? What is the problem? I can't afford a new water heater for at least six months and I'm tired of cold showers.
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Old 09-24-2017, 04:27 PM   #2
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Re: Cannot light the water heater pilot light


I don't think I understand.
You titled your post as can't light the pilot light. Yet you also say that you have confirmed that the thermocouple is in the flame.

Those two statements appear to be inconsistent with one another.
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Old 09-24-2017, 08:25 PM   #3
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Re: Cannot light the water heater pilot light


What I meant is that the end of the thermocouple is close enough to the gas tube that it would for sure be in the flame if I could get it lit. Thanks for your response.
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Old 09-24-2017, 08:52 PM   #4
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Re: Cannot light the water heater pilot light


You also said that you replaced the burner. I would think that if the pilot doesn't light while you are holding button down then you have a problem with the gas valve itself.
Are you sure you are getting gas to the valve? Do you have other gas appliances? Do they work properly?
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Old 09-24-2017, 10:33 PM   #5
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Re: Cannot light the water heater pilot light


Yes, the gas furnace works. After I hold down the buttion while trying to light the water heater I can smell the gas coming from the vent at the top of the water heater.

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Originally Posted by hkstroud View Post
You also said that you replaced the burner. I would think that if the pilot doesn't light while you are holding button down then you have a problem with the gas valve itself.
Are you sure you are getting gas to the valve? Do you have other gas appliances? Do they work properly?
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Old 09-24-2017, 10:47 PM   #6
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Re: Cannot light the water heater pilot light


While holding down the button for just a few seconds (don't flood the chamber), try lighting it with a long match or a butane lighter.

(Although you say you smell gas, there might be a chance that you are still pushing air, or that something in your burner assembly is not putting gas in close proximity to the igniter.)
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Old 09-25-2017, 12:06 AM   #7
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Re: Cannot light the water heater pilot light


Has the gas line been opened? In other words, could you have air trapped in the gas line?
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Old 09-25-2017, 12:27 AM   #8
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Re: Cannot light the water heater pilot light


I was able to light the pilot with a long butane lighter. It worked for one cycle to heat the water to the correct temperature, and then the burner shut off as it's supposed to. However, at that point the pilot also went out. So now the problem is I can light the pilot the hard way but it won't stay on.

The gas line has not been opened. If for some reason there was air in the line I assume it's no longer there.

The pilot and the pilot gas tube are 1/8" apart. I'm sure it's that because I measured it the last time I had the burner assembly removed.



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Originally Posted by MTN REMODEL LLC View Post
While holding down the button for just a few seconds (don't flood the chamber), try lighting it with a long match or a butane lighter.

(Although you say you smell gas, there might be a chance that you are still pushing air, or that something in your burner assembly is not putting gas in close proximity to the igniter.)
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Old 09-25-2017, 01:15 AM   #9
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Re: Cannot light the water heater pilot light


Sounds like thermocouple. You said you replaced the thermocouple. Is thermocouple well attached to the gas valve (screwed all the way in)?
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Old 09-25-2017, 01:39 AM   #10
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Re: Cannot light the water heater pilot light


Yes, screwed all the way in, and it's a new part. I suppose it could be defective. I found instructions online about how to test a thermocouple with a multimeter. I'll try that tomorrow.


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Originally Posted by hkstroud View Post
Sounds like thermocouple. You said you replaced the thermocouple. Is thermocouple well attached to the gas valve (screwed all the way in)?
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Old 09-25-2017, 07:55 AM   #11
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Re: Cannot light the water heater pilot light


Did some Googling,
Saw you post on another site. Also saw someone else who got it to work temporarily by leaving couple of the screws in the cover plate a little loose (for oxygen).
Might want to browse that site again.
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Old 09-25-2017, 08:25 PM   #12
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Re: Cannot light the water heater pilot light


Quote:
Originally Posted by hkstroud View Post
Sounds like thermocouple. You said you replaced the thermocouple. Is thermocouple well attached to the gas valve (screwed all the way in)?
AND>>>> Is the thermocouple in the PILOT flame.

(It may be working perfectly if the thermocouple is not being heated sufficiently by the pilot.... that's how it's supposed to work and shut down all gas flow.)

It is also possible you have a strong up/down draft blowing out the pilot intermittantly...and consequently the thermocouple trips all gas and you have to go thru a relite process.

Have you had any strange draft situations like strong winds or new combustion air supplies..... your chamber should be baffled from them, but not always.

About all you can due is relight everything, and when it shuts down, see WHEN the pilot goes out... that ill tell us something.

Good luck
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Old 09-25-2017, 11:03 PM   #13
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Re: Cannot light the water heater pilot light


I had a guy who works on a lot more gas appliances than I do, tell me he always kept a fine emery cloth in his tool box. He would polish the thermocouple and it worked better after that. I have never tried that, because I have never had much trouble with thermocouples.

I have had to adjust where the flame impinged on the thermocouple to get the thermocouple hot enough to work. I have been told that too much flame impingement could burn a hole in the thermocouple. I have not had that problem though
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Old 09-28-2017, 11:41 PM   #14
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Re: Cannot light the water heater pilot light


Thats a series 100 AO smith.. The corderite disks clog. But you said you cleaned it.. Was this unit underwater some? If so the disk swells and will not let air in. The issue when it starves for air is the chamber overheats. On the thermo couple these is a thermister. When this overheats it shuts the gas off. When it cools down it can then be relit...

All the money you spent on repair guy, burner and what not you could of had a new heater..

Thats series 100 heater is obsolete...

http://www.supplyhouse.com/AO-Smith-...-Model-Nat-Gas
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