Can I fix my own furnace?
November 28, 2007 4:20 PM   Subscribe

Help! It's cold and my furnace is broken. Since it doesn't have RAM, a PCI slot or a motherboard, I am clueless. Are there any manageable troubleshooting activities I might try on my own before I become a meat popsicle?

I don't know things about furnaces. I have the the user manual here, and best I can figure it's a Model 376C Downflow Horizontal Furnace from Bryant / Day & Night / Payne. The manual opens by welcoming me to a new generation of comfort, and I must say, based on my current level of cold, I find this suspect.

So, things that I know / have done follow:

This is a furnace with an electronic ignition. It doesn't have the pilot light like the furnace we had when I was a kid. Instead, the pilot light appears to be some sort of filament or something. The furnace turns on, and, when the thermostat is activated, the pilot light clicks on with a welcoming orange glow. This should, in theory, then activate the main burner with a gratifying "Fwooosh." However, it does not. Instead, the pilot 'light' stays on for a couple seconds, and then powers down. It then attempts to activate and light the main burner twice more. After it fails at these attempts, the furnace goes into a "lock down" mode, where it will not function again until I turn it off and turn it back on - this is not a malady, it is a feature.

I have put in new filters. This has had no effect. I have tried turning off the gas valve, turning off the gas valve control knob, cutting power to the unit, and then letting it sit for ten minutes before restarting it. This has had no effect. I have tried cleaning out the relief box and the gas burner with compressed air, based on something I read in the manual. This has had no effect.

So, barring that, is there a "fix me" switch or some other maintenance step I might perform that will not blow me up but might resolve this issue? Or, ok, maybe not resolve it, but might point me down the right path?

Thank you for your time.
posted by kbanas to Home & Garden (25 answers total)
Not to alarm you, but furnaces have safety features, and it sounds like something is tripping yours up. To me is sounds like something is interrupting the flow of gas

Unless someone answers who really knows what he or she is doing, I would contact your gas company to find a repair person sooner rather than later.
posted by gesamtkunstwerk at 4:30 PM on November 28, 2007

You know where the water shutoff is to your place, right? Just in case--be prepared to protect yourself against frozen pipes.
posted by gimonca at 4:32 PM on November 28, 2007

Stupid follow-up but like the support guy who asks if the computer is plugged in…propane or natural gas? If propane, is the tank empty?
posted by Dick Paris at 4:33 PM on November 28, 2007 is the place to go for this stuff, failing any other specific advice.
posted by autojack at 4:34 PM on November 28, 2007

Response by poster: Dick Paris,

It's natural gas.

Thanks to everyone for all your suggestions / answers thus far. I do have a repairman on call, but they won't be out until tomorrow, so while I waited, I figured I would probe the juicy innards of the hive mind to see if there was something obvious I might have missed.
posted by kbanas at 4:38 PM on November 28, 2007

second the empty gas suggestion
posted by Salvatorparadise at 4:40 PM on November 28, 2007

*not a furnace expert*
Does the fan kick on first?
We have a similar type of furnace, and the usual order of events for ours (as I recall) is fan/filament/fwoosh.
Maybe something's wrong with the fan which is tripping a safety shut-off? /pure speculation.

My other main appliance troubleshooting technique is to look for burnt/melted wires or components.
You've probably done that already though.
posted by dan g. at 4:40 PM on November 28, 2007

Did you pay your gas bill?

Just asking
posted by kanemano at 4:41 PM on November 28, 2007

A few questions to verify:

Is the pilot "light" (a filament) currently functional as far as you can tell? (above, it is unclear if you are describing how it is working or how it should work).

Do you have any other gas appliances that you can use to verify that you have functional gas service to the home?

Since there is no gas-driven pilot light, you can safely attempt to light any gas flow manually. Do what you would normally do while watching the filament, but put in a flame source (like one of those extended butane lighters) in the gas flow when you see the filament being heated.

Typically a problem like this actually has the flame come on, then go out because the unit does not detect a flame. With no ignition in the first place (and a seemingly functional ignition source) the upstream gasflow is a likely culprit.

With that information, you can probably contact your gas service to have them inspect the issue. They do gas detection and pilot-lighting all the time. It is likely that you can even do it cost-free.

Best of luck!
posted by milqman at 4:42 PM on November 28, 2007

Response by poster: milqman,

Well, ok, so, there are three... things.. (that is very descriptive, I know) .. they're basically like.. I don't know.. tubes, I guess? Each one kind of looks like a miniature trumpet... the manual refers to them as gas burners.

And at the end of *one* of these gas burners is the filament. When I activate the thermostat the fan kicks on and, after a number of seconds, the filament begins to glow a brilliant orange.

It is my impression that this should ignite the gas across the three gas burners, and that this should then ignite the main burner.

However, it does not. The filament lights up, there is a "click", and then the the filament goes off.

This repeats three times, and then things go dead.
posted by kbanas at 4:50 PM on November 28, 2007

Do you have a digital thermostat? Are you sure it's working? Check the batteries, and then make sure the temperature is set to a level that will kick the furnace on. It won't turn on if the therostat isn't telling it to.
posted by cosmicbandito at 4:51 PM on November 28, 2007

Response by poster: As to other questions, yes, our oven is uses natural gas, and it works just fine, so there shouldn't be an issue with the gas supply.
posted by kbanas at 4:51 PM on November 28, 2007

seeing your latest message, it sounds like you're not getting any gas. Be sure all of the valves are open in the gas line. Other than that, call the gas company and let them know you're not getting any gas.
posted by cosmicbandito at 4:52 PM on November 28, 2007

I'm guessing there there may be some sort of issue with a thermocoupler. These are in place to make sure that the gas turns off should there not be a flame (thus making sure that your house doesn't fill with gas and kill you/explode)....

You need a repairman.. put the energy tonight into making sure water pipes are drained (if it is below freezing in the house/basement/crawlspace)...then find a space heater or get a motel room..
posted by HuronBob at 4:55 PM on November 28, 2007 [1 favorite]

Response by poster: cosmicbandito,

It does indeed sound like an issue with gas, I agree. I made sure the valve on the gas line was set to open, and, like I said, the oven works.

Also of note, when I was cleaning out the gas burners with compressed air I did catch a whiff of gas, which leads me to believe that there is at least *some* gas coming down the pipe.

Is there a component in the furnace which typically regulates gas flow?

I want to try milqman's idea of trying to light the flow manually, but my girlfriend has completely forbidden it, because she is convinced it will blow up the house.

posted by kbanas at 4:57 PM on November 28, 2007

Response by poster: HuronBob,

You're right, I know you're right... there's.. just something in me that is really pissed off at my inability to fix this.
posted by kbanas at 4:59 PM on November 28, 2007

Best answer: careful!
posted by Salvatorparadise at 5:04 PM on November 28, 2007

Sounds like the solenoid valve for feeding gas isn't being tripped. Either the solenoid is bad and will have to be replaced (coil is open, or the mechanical parts of the spool valve are stuck, possibly on a bit of pipe scale that has worked its way into the spool), or the signal it needs to open isn't being delivered (most likely cause is a defective controller board). You can tell which of these possibilities is true with a multi-meter, put across the soleniod's coil. If voltage is present across the coil when the gas should be flowing, the solenoid is bad, otherwise the control board is defective, or there is some error condition causing the controller to fail sending a signal to the solenoid.
posted by paulsc at 5:07 PM on November 28, 2007

Response by poster: paulsc,

Come to my house and do this. Please? :)

No, ok, I've posted to, and I appreciate you guys posting all this information. It is very helpful. At the very least, one the repair guy (or gal) comes out tomorrow, I will be slightly less ignorant than I was when I started this thread.

I think I'm going to close everything up and wait for the cavalry.
posted by kbanas at 5:11 PM on November 28, 2007

I'm with paulsc:

Your issue is almost definitely upstream gas. If your lighter flame is there before the the unit kicks on there will be no stagnant/collected gas there to "blow up the house". When it kicks on, the gas should come in soon after the ignition filament gets hot. If it does not, there is either a solenoid (mechanical) problem or a controller (electrical) problem.

Regardless, I am fairly confident that having a lighter anywhere in there at the moment the gas starts will result in nothing (because the gas isn't getting there in the first place). It is probably one of the first troubleshooting steps a repairman will do anyway.

Blankets are an ok fallback :)
posted by milqman at 5:34 PM on November 28, 2007

Most newer gas furnances have a electric fan/blower to provide draft. If this blower is not working (and you should hear it if you are near the gas parts) the gas valve will not open. There is also a switch a little higher in the flue, that has a little "sail' on it to detect if the draft is strong enough, if this switch is not working there will be no signal to open the gas block. You should be able to hear the fan come on before the igniter coil heats up (glows). I don't know of a easy test for the sail switch. Neither are "fixable" parts, they need to be swapped out. Sorry...
posted by digital-dragonfly at 5:38 PM on November 28, 2007

I got money on what they call the roll out / flame out switches . Mine did this once before - same thing you are seeing. There are these sensor type switches that detect if the flame comes out of the heater box (i.e. they are testing temperature). They get old over the years (they take some abuse - hot dry air blows over them constantly). Your manual may show where they are - but there is a reset button on top of them that you can press to reset the switch.

Big caveat here - if those switches are tripping for a reason it is because the flame is making it outside of the box - very dangerous. You will find one where the heated air exits your furnace unit.

Mine had gone bad - I had to remove the switch and just wire the two wires together - until I could get a new switch in the morning.

Please be careful - if this above your skill level wait until tomorrow - you are dealing with dangerous things as I am sure you know.
posted by jaythebull at 5:53 PM on November 28, 2007

You likely have an induced draft furnace. There is a small blower next to the exhaust flue that assists the flow of combustion gases through the heat exchanger (not to be confused with the large blower that pushes air through your house.) There is a diaphragm pressure valve that senses the negative air pressure in the flue when the inducer blower is running. If it doesn't detect the pressure of the blower it won't turn on the gas because the it thinks the fan has failed or the flue is blocked. Usually what happens is that the port in the flue through which the air pressure is sensed becomes plugged.

First turn off your furnace by flipping the AC switch at the furnace. Take off the upper front panel of your furnace. You should see something that looks similar to the picture here.

See the small inducer blower motor on the left and the plastic tube leading to the pressure switch on the right. It is possible that the flue opening has become plugged with dirt blocking the pressure valve. Often this is because of rust or dirt in the connection to the flue. First remove the tube from the pressure valve end by sliding it off, leaving the other end connected to the flue. Then see if you can suck or blow air into the flue. The opening into the flue is very tiny, sort of needle sized, and smaller than the tube itself, so don't expect to be able to blow much air but it should not be completely blocked. One way to tell is to suck hard and then block it with your tongue. If you tongue sticks, no air is able to get through. If it is blocked you will have to disconnect the tube on the left and poke a stiff wire or needle to clear the blockage. This is usually rust so it can take a lot of force to clear the blockage. Remember that the opening to the flue is a tiny needle hole in the very center of the flue fitting. Then replace the tube and suck again to check if it has been cleared. Reattach the tube on both ends, turn on the AC power and your furnace should now run.
posted by JackFlash at 6:07 PM on November 28, 2007

Oh, and just one more caution. Don't poke a wire into the pressure valve because you will damage the diaphragm. Only poke the other end where the tube attaches to the flue. The pressure valves themselves rarely fail.
posted by JackFlash at 6:22 PM on November 28, 2007

Response by poster: JackFlash,

Thanks so much! That's a lot of great information. You guys are great. Seriously. If any of you want some chocolate chip cookies or something drop me a mail and I will be more than happy to make some and send them out!

My furnace is STARTED!

I don't really understand how, however. I mean, I looked at the picture JackFlash provided, but my furnace is not configured in an identical manner and the things he pointed out were not user accessible without taking apart a lot of other things (to use the technical lingo).

I mucked around inside and plugged and unplugged some things and found the draft reset switch and hit it and gave it one last chance reboot and it fired right up.

What the fuck.

Thanks again you guys. You're so amazing. !
posted by kbanas at 6:51 PM on November 28, 2007

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