Gas furnace not turning on?

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  #1  
Old 02-28-08, 05:13 AM
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Gas furnace not turning on?

Hi. I built a home two years ago and was persuaded to put in a gas furnace and water heater instead of electric ones, like I'm used to. Now I have an issue.

Over the last couple of months, it's been particularly cold here (obviously) -- averaging around 20-25 degrees between the highs and lows. I've been experiencing a problem with the furnace. (Please excuse my layman's terms, since I don't know much about furnaces.)

If I have my thermostat set to 73 degrees, and it drops below that in the house, the heat, of course, tries to kick on. Usually it does just that with no problems. I typically hear the thermostat click, signifying that it has turned the heat on (and indeed it says "Heat On" on the thermostat). Then I can hear what I assume to be the furnace "starting up." After a few seconds, I usually hear something that sounds like a flame catching (maybe from the pilot light?), then the heat comes on, and all is well.

But a few times in the last couple of months, a different scenario has occurred. When the problem occurs, what happens is that I hear the furnace "start up," but nothing ever "catches." Then, after about 20-30 seconds or so, the furnace sounds like it powers down. Then it powers back up again, trying again. (A lot of times, it "catches" on this second try.) If it doesn't catch the second time, it'll try for a third time. If it doesn't catch the third time, it just turns off and doesn't try again. Now, the bad thing is that my thermostat still reads "Heat On," so I guess it thinks the heat is actually on, even though it's not. One time a few weeks ago, my thermostat was set to 70 degrees and it got down to about 63 before I noticed something was wrong.

I never sat long enough to figure out whether it ever tried again (after the three initial tries) or not, until this morning. About an hour ago, the furnace tried to turn on three times, failed, and quit. Just a few seconds ago, it tried to turn on again and worked. I'm not sure whether the downtime is set to an hour between tries or what.

Usually I can kickstart it by turning the heat completely off on the thermostat and then back on again. But I worry that one wintry stretch, I'll be away for several days and my heat won't ever come on and my pipes will freeze. Is there something wrong with my furnace or is this normal?

Thanks for all your help!
 
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Old 02-28-08, 08:22 AM
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It's not normal. You could have one of many things going on. 1st, how is the air filter ? If the air filter is clean you're gonna have to go to the furnace and let it run through a cycle and write down exactly what it does prior to not running properly. On a call for heat you should get a exhaust fan on 1st, then the burners should light, then the main house blower should come on.
 
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Old 02-28-08, 08:29 AM
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The air filter is clean. I buy the cheap ones and replace them every 30 days, as instructed.

I never know when this is going to happen -- it could be weeks in between, for all I know, so how can I write down what happens before it screws up?

Originally Posted by mattison View Post
It's not normal. You could have one of many things going on. 1st, how is the air filter ? If the air filter is clean you're gonna have to go to the furnace and let it run through a cycle and write down exactly what it does prior to not running properly. On a call for heat you should get a exhaust fan on 1st, then the burners should light, then the main house blower should come on.
 
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Old 02-28-08, 02:48 PM
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Sounds like the ignition process is just not here for you. You need to tell us if you have direct spark to burner, or a glow type ignitor, or a pilot flame that is supposed to come on first.

And then report what you see happening or not happening in the start up sequence; like does any the ignition try to come on? Or does it indeed come on and then the burner comes on, but goes out in 3-5 seconds?
 
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Old 01-03-09, 04:31 PM
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I don't know much about furnaces, so please excuse me if I don't describe using proper terminology. However, I am having the exact same problem as abbyqueue described in her initial post.

I tried turning the thermostat to 'off' and then back to 'auto'. The furnace starts and there's a round plastic panel near the top half of the furnace about the size of the quarter through which I can see an orange flame. However, the flame dies down and then the furnace tries it again for three times total. After that, it doesn't do anything unless i reset the thermostat again.

I have a goodman high efficiency 95% furnace with 2 stage motor and it's only 6 months old. I'm waiting for a service tech to come, but I'd appreciate any insight as it's freezing right now.

Thanks
PJ
 
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Old 01-03-09, 04:49 PM
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Just to update -- I did not solve this problem, only because it hasn't happened to me since.

So far this winter, I have not had the furnace malfunction in this manner, but I'm sure it's only a matter of time, so I'm curious as to PJ's solution!
 
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Old 01-03-09, 05:46 PM
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These are the symptoms of a furnace on the edge of failing. Odds are, before very long it will quit working and wont turn on at all.

Especially with a new furnace, I would expect you have a warranty and you should have the heating contractor come out to inspect and repair the equipment.

And it's not acceptable for the repairman to switch it on, say "it works now--- nothing I can do" and walk out. There is lots he can do. beginning with:


This sounds like an intermittent failure of the circuit board to detect the presence of the burner flame. Measuring the flame sensor circuit tells you if you are getting a good signal (4-5 micro amps) or a marginal signal (1/2-1 micro amp) checking again after cleaning the flame sensor tells you if that was a likely cause of the problem (increasing the current from 1 micro amp to 4 micro amps, for example.

If the flame sensor current was good, he should cycle the furnace through the ignition cycle 40-50 times to see if he can get it to fail when he can observe the problem.

(incidentally, that something you can do as well --- cycle the furnace on a bunch of times and see if you can detect a pattern to the failure.)

There are other things it could be, but the pattern of the three attempt at ignition followed by the lockout is typical of a furnace flame failure problem.

In my view, if the flame sensor current is good, they really ought to replace the circuit board under warranty. That would be the highest probability of the cause of the problem, and you don't want to get stuck with the cost of replacing an expensive part after the warranty has expired by a few months.


So my recommendation is be proactive! Expect to get good service from your heating contractor and don't let them get off by saying "Well, it's working OK now." That's the lamest excuse around for a repairman.

Intermittent problems are the bane of repairmen. Poor excuses for a repairman ignore the difficulties when they can with excuses like the one above. Good repairmen realize they have to use all their skills and experience, and probably a good deal of time, to cause repeats of the problem and to tease out the cause of that problem.

Because it's rare that they get better on their own. Usually they get worse over time and leave customer cold sooner or later.
 
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