Furnace went dead too soon!

April 11, 2010 10:52 AM

Furnace broke (2 weeks too soon) I have a relatively new Lennox in the basement that was recently looked at, and I was told it was in Perfect Condition. The other day it went totally dead! Flipped all breakers, switched it on/off several times, and no power getting to it. I'd like to fix it myself, where do I start, I'm imagining some sort of step by step troubleshooter? The web has been surprisingly unhelpful so far. Thanks everyone for any advice or help.
posted by Benzle to Home & Garden (11 answers total)

Oil/Gas/Electric/Wood? Forced air? You say there is no power getting to it. Did you ascertain this with a meter? Have you tried bypassing the thermostat?
posted by Mitheral at 11:37 AM on April 11, 2010

Do you have the manual? My furnace (also a new Lennox) has an access panel, and under that is the main circuit board. There's an LED that blinks in different patterns depending on the error condition. Even if you don't understand the error code at least you'll know the thing isn't completely dead!
posted by miyabo at 11:51 AM on April 11, 2010

There is really no way to help you unless you tell us some more. First, is it an electric furnace? Is the a second fuel (perhaps gas) involved and the electricity is just to drive fans, etc.? You say you flipped breakers. Is there a double breaker at the main panel that is dedicated solely to the furnace? Is there another breaker (perhaps a disconnect right next to the furnace)? This disconnect might be one that pulls out, exposing two fuses each the size of a shotgun shell. What makes you say, "...no power getting to it..."? Is this simply because it doesn't turn on or did you put a meter to the lines?

I'll be back in twenty minutes or so.
posted by Old Geezer at 12:17 PM on April 11, 2010

Without your input, here is the best I can do for you. If you have power all the way to the furnace and the LEDs are blinking, you probably don't have any options but to call a Lennox repairman. You most likely have a gas furnace with electronic controls. There are any number of ways they can go bad, including fried circuit boards, dirty flame sensors, etc., etc., and so forth. Unless you have been to furnace school and looked inside several of these you are not going to find anything in there that you can work on. BTW, Lennox does not sell parts directly to the public, probably due to liability issues. If you start mucking around in there you are likely going to void any warranty that may still exist on it.
posted by Old Geezer at 5:38 PM on April 11, 2010

Like you, I'm a home warrior who enjoys tackling projects like furnaces and hot water heaters. But in this case, I think it would be wise to call the repairman, especially since your furnace is fairly new and (hopefully) still under warranty. You really don't want to mess with it and find out you've voided your warranty.
posted by exphysicist345 at 6:04 PM on April 11, 2010

Response by poster: Ok, 1st. question, It is gas and yes I tried bypassing the thermostat, but there is NO power getting to the unit, so of course had no effect.
posted by Benzle at 6:48 PM on April 11, 2010

Response by poster: 2nd, response: Crazy! I say that there is NO power getting the the unit and the first two responses totally ignore this. Yes the blinking green LED would be helpful in diagnosing the problem.
posted by Benzle at 6:50 PM on April 11, 2010

Can you tell if there is power after the main fuse? I had a similar situation with a new furnace last year. I could tell that there was power after the first fuse (by using a voltage detector), but inside the furnace there was none at all. In my case it turned out that there was a blade fuse on the circuit board itself, which was blown (due to a loose unused thermostat wire causing a short).
posted by everybody polka at 7:02 PM on April 11, 2010

blown transformer at the furnace? my boiler has a 12v or 24v (I forget which) transformer that went dead. I diagnosed the problem with a multimeter.
posted by malp at 7:03 PM on April 11, 2010

There's two flavors of electricity for a furnace - 110 or 220V (to make the fan go) and low voltage to run the circuit boards. On mine the transformer (as polka describes) is mounted on the rafters with a small wires running control power to the unit. Check the output side of the transformer and if that's live check the places where those wires lead to.

My bet is it's your transformer, a fuse in that initial circuit, or a relay of some sort that isn't relaying any more.

Be careful because there might be a few high voltage connections in there that aren't as dead as you suspect.
posted by Kid Charlemagne at 9:47 PM on April 11, 2010

Being hostile to people attempting to help won't get you very far. You say there is "no power", but a lot of people would say that for varying values of "no power". If you were such an expert that we should have confidence in the meaning of "no power to the furnace", then you would have an electric problem, not a furnace problem.

With forced air furnaces, the most likely failure is in the exhaust blower. Specifically, a temperature-sensitive breaker. If that breaker fails, the furnace will not be responsive. If the blower itself fails, the furnace will ignite, then shut down when the breaker gets hot. A new blower shouldn't fail. A breaker might. Jumper the breaker, the furnace should run, and you know it is that breaker that needs replacement.

This system is important, and you should in no way operate the furnace unattended with the breaker jumped. The exhaust blower is to prevent carbon dioxide and carbon monoxide from building up in the room, and part of what enhances the efficiency of modern furnaces.

A friendly repair service might be willing to sell you a replacement breaker, to make the repair yourself.
posted by Goofyy at 1:55 AM on April 14, 2010