i’m proud of myself for getting around to this before november. 🙂
last spring, my 24 yr old gas furnace kept going out. i’d re-light the pilot, and then when i turned the control from “pilot” to “on”, a big whoosh of gas would ignite the burner, but blow out the pilot.
anything i can do, short of replacing the whole thing?
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Replies
Disreguarding the any problems with the current furnance the increased efficiency of a new furnace makes it "time" to replace.
In most cases a problem like yous is not a difficult problem to fix. Dirty burner, misadjust burner or blocked flue.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
thanks bill.
i understand the potential savings, but i'd like to get one more year out of it.
any hints on adjusting the burner?
>>any hints on adjusting the burner?Get yourself a combustion analyzer, learn how to use it, learn about your model furnace, and have at it.Or look for a trained HVAC combustion analyst near your zip code at http://www.nationalcomfortinstitute.com
In Xanadu did Kubla Khan
A stately pleasure-dome decree
Where Alph, the sacred river, ran
Through caverns measureless to man
Down to a sunless sea.
Coleridge
In addition to the problems Bill mentioned, we had similar problems with our old furnaces that turned out to be due to having the pilot light adjusted too high. If it's adjusted so high that the base of the flame stands away from the pilot jet then it's easily blown out.
thanks dan.
i've adjusted the pilot. the problem isn't that it blows out easily, it's the big whoosh of gas upon ignition that blows it out.
Backflashing is a pretty common problem with gas appliances. It's generally caused by an air/fuel ratio problem -- either too much air, or not enough. Probably the latter. Causes range from those BillH mentioned, to bad valves, defective burner parts, pilot mis-placed with respect to the burner, drafty or air-starved combustion chambers, etc. Hard to say how to fix it. You just need to try to figure out why there is not enough air mixing with the gas before it gets to the pilot.
If you can't figure it out, it may be wise to call in a pro to diagnose and repair it. Left uncorrected, backflashing can get pretty serious.
Mike HennessyPittsburgh, PA
What Mike said. In addition, some valves are "step opening", where they open partially for a few seconds and then open fully. If the dashpot or whatever that times this is worn then the valve will open rapidly and you can get too strong of a "whoosh".
Too much sanity may be madness. And maddest of all, to see life as it is and not as it should be! --Miguel de Cervantes
What all posters have said is correct AFIK, just wanted to add that your problem is probably not due to a crack in the heat exchanger, probably burner adjustment issues.
You have to make sure if you have an older furnace that you do not have a crack in the heat exchanger. You have to check with a mirror and a light, and be very careful and methodical in your inspection.
What happens with a gas furnace is the flame burns inside the heat exchanger and exhaust goes outside up the flue, if heat exchanger gets a crack products of combustion (exhaust, deadly carbon monoxide as well as Adlehyde gas) can be introduced into the living space. Headaches, feeling lousy, respiratory health issues, death.
If you've got an old one check it with mirror and lights as careful as you can for cracks.
Actually, very few cases of co are caused by cracked heat exchangers.
Having said that, a cracked exchanger needs to be replaced.
i will agree that it is rare, but not nearly as rare in older furnaces, each grade of steel will have its own fatigue limit, and it can reach that limit by the repeated cyclings over the seasons with the expansion and contraction of heating and cooling.
its only a matter of time for all of them, some will last 130 years, but some are going to start failing at a much higher percentage after 20 years. the statistics are all over the map, but as a service person checking old furnaces any sign of a crack on the heat exchanger gets it replaced.
I believe rich1's point is that even with a crack a heat exchanger in a conventional FA furnace is "unlikely" to leak significant amounts of CO. First you have to have poor combustion, leading to the production of large amounts of CO, then you somehow have to get that CO to flow through the crack even though the pressure gradient is in the other direction. Two relatively unlikely events producing one that is much more unlikely.My general observation (including some personal experience) has been that CO problems are far more commonly caused by some sort of flue obstruction.However, having said that: Yes, if the HE is cracked the furnace should be scrapped. Even "unlikely" is too much of a chance to take.
In science it often happens that scientists say, "You know that's a really good argument; my position is mistaken," and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion. --Carl Sagan
Thank you, I was missing that point entirely.
One glaring exception is the old Lennox counterflows that had a piece of angle iron welded just above each hx. The angle was intended to direct the air around the hx, but it also created a venturi. Had one with a bunch of pinholes at the very top just below the angle which caused the exhaust gases to leave the hx and enter a school classroom.
Thank goodness no one got sick.
That is scary, kids are most affected by stuff like that.
Once the burner is lit, blowing out the pilot shouldn't be a problem. The unit hasn't reached a temp to start the blower fan at this point.
Does the unit have an induction fan?