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AO Smith boiler. Pilot light goes out spuriously. Combustion air starvation?

AO Smith boiler. Pilot light goes out spuriously. Combustion air starvation?

Old 10-08-13, 07:17 PM
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AO Smith boiler. Pilot light goes out spuriously. Combustion air starvation?

I bought a house with an AO Smith ProMax 50gal water heater, and the pilot light (and burner) seem to go off at random times (flameout), at which point I have to relight it.

After reading this very helpful post http://www.doityourself.com/forum/wa...water-hot.html , I realized the most likely cause was insufficient air supply to the combustion flame sealed chamber.

Sure enough, I cleaned the ceramic filter underneath as suggested, using the very helpful method suggested by “lawrosa” with a bent piece of flexible copper tubing. However, the filter was not really dirty, and the general area under the filter was rather clean.

Reliability improved, but I still got spurious flameout events and I would have no hot water, have to relight the pilot – and wonder.

Further investigation:

Through experimentation, I discovered that I got less spurious flameouts if I removed the first air filter screen (the black plastic one) and then got almost no flameouts if I also removed the orange rubber hood that seals the gas tube entering the combustion chamber. This seems to indicate that the heater still has an air starvation problem. Of course, I do not intend to run this heater with the first air screen and rubber seal removed since doing so breaches the combustion chamber isolation and dust arrest mechanisms, and I do not recommend it -- but I did so temporarily, for diagnostic purposes, keeping an eye on it. I tried several times and with the black plastic screen and rubber seal in their intended position I get flameouts. There just isn’t enough air flow into the combustion chamber.

I checked the exhaust flue, and it does not seem to be obstructed. I thought that if it were obstructed then hot air would come out from the typical air gap at the top of the heater / flue interface. But no air comes out of that gap and there is a healthy flow of fresh air into the gap and out of the flue.

So I did some more research online and found plenty of similar issues with these AO Smith heaters (eg. here 240 Complaints and Reviews about A. O. Smith Water Heaters | Page 7 – Actually most complaints about AO Smith boilers on that page are about this flameout problem issue).

So it seems that this heater design is defective, as the air supply into the combustion chamber seems marginal, and apparently any perturbation from the original “brand new” heater condition triggers this combustion oxygen starvation problem. Either that, or the flame air starvation safety mechanism is overly sensitive, …or something else I’ve yet to discover.

So I’m wondering. Is there any type of AO Smith retrofit kit that would fix this problem? Or a kit from a third party supplier?

I see that there is a replacement external dust screen that wraps around the heater and apparently replaces the smaller black plastic screen. It has a bigger total area, so it should block airflow less. However that would not be sufficient to fix my situation (and many others, I suspect) since even removing the black plastic screen completely is not quite sufficient in increasing combustion airflow, , I must also detach the orange ruber seal where the gas line enters the combustion chamber to provide sufficient combustion airflow.

Needless to say, I do not want to run this heater with the black plastic screen and the rubber seals removed, even though that would simply create a situation similar to what all water heaters had before this sealed chamber (mandate?) appeared.

The other thing I read is that perhaps AO-Smith is supplying a different thermistor, apparently one that is less sensitive (200C as opposed to the originally installed 180C ?) so it could also be an issue of too sensitive an oxygen starvation sensing mechanism.

In summary, I need to solve this oxygen starvation safety mechanism trigger issue. I see 4 main possibilities:

a) Somehow increase air supply into the chamber (safely, not by removing filters and seals)

b) Perhaps decrease the gas flow. In principle, a smaller flame will need less air, perhaps getting around this insufficient combustion air problem – will take a little longer to heat, but I can live with that, compared to the current surprise flameout and cold morning shower.

c) Decrease the sensitivity of the oxygen starvation safety mechanism, if indeed the problem is simply unnecessary oversensitivity

d) Junk this heater, accept the fact that its design flaw is unfixable, and get a new heater (probably not an AO Smith given the bad experience, though it may not be AO Smith’s fault -- we may have asked for this ourselves as consumers/voters).

So, out of curiosity, is this sealed combustion chamber design something that AO Smith did on its own initiative, or did we “The People” collectively decide to get into the water heater design business by requesting and imposing that the government energy commissar impose this on heater manufacturers ?

Any advice appreciated.
Old 10-08-13, 07:42 PM
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) Junk this heater, accept the fact that its design flaw is unfixable, and get a new heater (probably not an AO Smith given the bad experience, though it may not be AO Smith’s fault -- we may have asked for this ourselves as consumers/voters).
That would be my advice....................

AO smith was /is ahead of its time. They are the leaders IMO. What you see is what all manufactures will have. Although there was some bad technology and the cordirite disk flame arrester was one of them...

I would not buy anything but ao smith.....Just me maybe
Old 12-15-13, 08:55 AM
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Lightbulb Increase the Oxygen Supply With a Table Fan on the Floor

CAVEAT: I'm a systems scientist with NO HVAC training. This means (a) I go at a disturbance from lots of different perspectives, and (b) my new solution may invite a fresh problem when the old one is contained. That said, here's what my experimenting with A.O. Smith pilot light flameouts accomplished for me.

Gas pilot flameout is only the symptom not the disease. The combustion chamber oxygen starvation problem in A. O. Smith boilers and hot water heaters has a cheap non-plumbing low-tech solution. It’s also safe for the homeowner to manage.

Put a table model electric fan on the floor beside the boiler or water heater. Aim the fan under and around the pilot light’s combustion chamber. Turn the little fan on low speed, without gusts or sweeps. Turning the fan on medium or high speeds can blow the pilot light out.

The steady gentle passing breeze keeps dust and lint from accumulating at the gas orifice, while increasing the supply of oxygen the flame needs. Pilot light maintenance by a trained technician then consists primarily of needling out the orifice -- to keep the blue flame’s shape symmetrical. Secondarily, the dust, lint, and debris stirred up by the steady breeze requires careful removal.

Blue flame symmetry indicates no blockage of the gas flow. Yellow flares in the pilot’s blue flame mean either some of the floating debris particles are reaching the flame to get burned, or else the flow of enough oxygen to the pilot light combustion chamber is not steady.

Dust, lint, and any other tiny debris should also be expelled and vacuumed out of (not blown into) tubing and areas reaching the pilot light’s combustion chamber. The technician must disassemble enough components to do a careful cleanout. Taking the apparatus apart and then putting it leakproof back together are not proper tasks for an untrained homeowner.

High cost servicing “solutions” like changing out the thermocouple or replacing the entire gas valve assembly can be costly useless ripoffs. Those procedures only address failures of microvolt flow or gas flow – but not oxygen supply or debris removal.

Replacing the entire furnace ($7,500??) when one small electric fan can prevent pilot light flameout is a swindle. A service technician’s income can depend on how much revenue he steers to his employer, so be very wary of the “comfort advisor” who follows the service technician.

Replacing one small Wal-Mart electric fan costs $10-$20. (A second fan blowing can raise too much breeze around the pilot light combustion chamber, so keep a small spare fan handy but not running.)

For added safety place the little electric fan on a shallow upside-down plastic pan, to keep the fan out of low water that might rise on the floor. (A dry plastic pan upside-down insulates, but a dry metal pan upside-down would conduct electricity to or from a wet floor.) For still more safety, buy a carbon monoxide detector to work near the table fan.

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