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Willams LP counterflow heater shuts down with "puff"

15 year old Willams 3508331 makes an increasingly loud puff or mini-explosion when finishing a heating cycle (when main flame goes out).
I don't think it is dangerous yet, but would like to know the cause.
Williams, LP provider and place I bought it only say to clean it, so I have removed the whole burner assembly and blown out with compressed air a twice with no effect.
Any ideas would be appreciated

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  • 10 more comments 
  • jimarm Jan 28, 2009

    Thanks for the quick reply!

    No carbon buildup; the cleaning did improve the flame patten some. No soot in vent.

    Whoof (good description) comes immediately after thermostat clicks off, sort of like a last gasp. I have not been able to see it, but I am sure it is flame/gas related, not metal contraction.

    The heater really just runs at night with approximately 1/2 hour cycles and the whoofs may increase toward the morning.

    As I said the heater has been working well for 15 years and this symptom is perhaps a month or six weeks old. It may be getting slowly worse.

    I have had to clear the pilot orifice twice in that period, maybe 7 years apart.

    Thanks again

  • jimarm Jan 28, 2009

    Thanks again for your time.

    1. Vent clear and capped

    2. No carbon or soot buildup in the vent pipe or heat exchanger

    3. I ran a cycle (the first one in two hours or more), watched the burner (getting quite warm doing so) until the thermostat was satisfied.

    Of course the flame was extinguished instantly and quietly. :=)

    That kind of goes along with my notion that it gets louder (worse) toward morning, after 15+ cycles.

    I also am leaning toward unspent fuel, perhaps from just a tired old valve that has cycled 50-100000 times. There certainly may be an adequate ignition source in the flame sensor area.

  • jimarm Jan 28, 2009

    I forgot to mention that the flame does NOT change when the fan comes on.

  • jimarm Jan 29, 2009

    Mr. Mark: It is a relief to find someone to help troubleshoot this problem, since Williams has decided not to provide technical assistance; sure makes me think twice about a Williams replacement, especially since I have been bummed by the loud fan since the first time it fired up.

    I am still just kind of anticipating what the future may hold, trying to figure out what is going on and when to think about replacing the control unit or the whole heater.

    I continually smell for any leaks and test with a bubble solution whenever I make any changes.

    I have a very old freestanding heater with ceramic elements above the burner that I have used, unvented, in the bathroom for 25 years (probably a code, if not a saftey violation) with a nearby CO detector. It has always made the same "puff" noise on closing its valve.

    Any more ideas or avenues of investigation will be appreciated.

  • jimarm Jan 29, 2009

    I finally got a look at the "whoomp" after hearing several times in the night.

    It is a fairly small burst of flame from the middle of the burner immediately after the gas supply is shut off at the end of the cycle.

    It looks smaller than it sounds.

    I will get the pressure tested, even though it is a fairly new unit.

    Otherwise, I'll just wait until the whole heater bulges out with each discharge.

    Thanks for your help. I rated it appropriately.


  • jimarm Jan 29, 2009

    Prelimiary report:

    Even though my LP range was not showing anything different, I thought to ask my LP provider (who had sold me a new regulator about 15 months ago) if there had been any problems or failures.

    The boss thought not, but sent a serviceman out in about two hours (great company!).

    The regulator consistantly showed 20" WP, when they were supposed to run at 13!

    So: new regulator (no charge) running at 13" and a better (less rich) flame pattern.

    I will hopefully post a PROBLEM SOLVED message tomorrow morning.

  • jimarm Jan 30, 2009

    You can imagine my chagrin and disappointmnet in having to report that the replacement of the faulty pressure regulator did not fix the problem I have been having.

    There is a chance the severity of the "whoofing" was diminished slightly and I suppose might continue to improve.

    I will try to figure a way to establish some kind of baseline to determine any change, positve or negative, in the situation.

    Thanks for the help and any new ideas.


  • jimarm Jan 30, 2009

    As I said in my first post, I have removed the burner assembly twice, wire brushed it and blew out with compressed air. There was minimal rust, but a fair amount of loose material blown out.

    Orifices are clear and flame pattern pretty good.

    The manual that came with the unit called for a pressure of between 11 and 13 WC, so I should be OK with the new regulator, i.e. the pressure can't be more than at the tank (13) especially after the run to the house.

    I will spend some more time simply watching the heater in operation; with the small possible improvement I am not ready to panic or give up.

  • Mark Egan May 11, 2010

    Well Jim,

    It's a business I've been in, in one way or the other, since Jr High (late '60's). I taught it at a local Jr College in the late '80's through middle 90's. I've been on the design side, and I've been on the service side. I' even have a good friend whom is a high up in Lennox, who didn't know anything about HVAC when we first met in the late 70's.
    I got out of it back in 1999 (am now in the material handling and conveying business, and have been breaking new ground there as I did in HVAC), but if I could find a HVAC manufacturer who would let me in, I would do it in a heartbeat. It's a business I have a true passion for, but one that I am too old to start into on my own again.

    Let me know if you have any more questions. I'll be happy to answer.

    As for the open flame ceramic, your right, they are outlawed and can no longer be manufactured, but you can still use it all you want. As for CO buildup, I doubt you have a tight enough space for that to happen (which was the reason the government used to cause manufacturers to cease production. New, tight, energy efficient homes, which would NEVER use that type of heater anyway. Go figure!).

    Thanks for the kudos though. It warms me up to know that I can be of help.

  • Mark Egan May 11, 2010

    You don't have a leak of some type that may be allowing LP to accumulate in the bottom of the closest do you?

    LP is heavier than air, so will lay in low areas.

    I know it's a reach, but something is just puzzling here.

    Number of cycles should have no bearing on it unless something like fuel pooling occurs when the unit cycles alot, but when it doesn't cycle, the pool get's chance to disipate.

  • Mark Egan May 11, 2010

    Your going to need to watch this thing to isolate where the "whoof" is coming from. Based on what your saying, it can only be caused by unspent fuel, whether it's the gas itself, or carbon buildup.

    Make sure the vent stack is clear all the way to the roof, including the cap. And make sure there is a cap.

    Remove the vent pipe from the furnace and look inside the heat exchanger from the top. Any carbon there?

    The draft induce motor should come on with a call from the thermostat, and should shut off when the thermostat is satisfied. All is controlled through the controller board. Make sure this is how the system is operating.

    Let me know what you find, good or bad. If good, I'll keep thinking on what's causing the problem. But without eye's on review by you, it's hard to isolate where the problem is.

    But if I had to guess now, I would be suspect of the gas valve. You might also want to observe if the flame character changes at the time that it first fires to begin heating the heat exchanger, and the blower comes on. That would indicate a failed heat exchanger, particularly with you comment of "it seems to slowly be getting worse".

  • Mark Egan May 11, 2010

    Have you watched the system to see where the explosion came from, and if you could see a sequence of operation that led up to the "whoof"?

    Did you find any carbon buildup inside the burner chamber side of the heat exchanger?

    Gas valves, whether LP or natural gas, must close without flutter. For their to be any residual gas in the heat exchanger does not make sense.

    Listen and watch where the furnace is and determine if the noise is gas related, or metal expansion/contraction related.



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And one last thought I forgot to put in the previous that you reminded me of -

LP or propane fired units do tend to backfire when they go out. Has to do with the residual gas pressure after the valve closes. My only suggestion is to have the gas pressure measured and the regulator at the tank adjusted. I believe it should be 9.5" -11.00" W.C (water column) but I would have to pull a book to remember for sure. Proper pressure will assure minimal backfire.

Posted on Jan 29, 2009

  • 2 more comments 
  • Mark Egan Jan 29, 2009

    Oh, and a FixYa rating would sure be appreciated if you don't mind. Or whatever you feel I'm worthy of.

  • Mark Egan Jan 29, 2009

    Thanks again, and be sure to have the regulator at the LP tank checked too.

  • Mark Egan Jan 29, 2009

    Your making me feel better with every post!

    I'm either guessing right, or something.

  • Mark Egan Jan 30, 2009

    Have you pulled the burners out and made sure they were clean?

    Do you see any excessive rust, flaking or not, inside the burner area?

    Make sure all the orifices in the burners are clean, and make sure the air port has been adjusted properly so you have a good strong flame. One that is sitting on the burners, but no yellow tip.

    You might also check the gas valve pressure in the furnace. There is usually a port on the manifold after the valve, or a port on the outlet end of the valve itself. I'll have to check to see what that pressure should be for sure.



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