My Ducane gas furnace is refusing to light, and it's getting COLD in here! Would love to call a tech but all are on emergency-only service for the holidays and I just can't afford that right now. Any suggestions on getting it to light just once would be great!

Some background - 13 year old natural gas furnace, brand new with house. A couple months ago I noticed that the pilot was kicking on and gas was lit for about 2-3 seconds, then I'd hear a noticeable click and it would shut off. Circulation fan would never start. After disconnecting some cables and troubleshooting, just sort of started working again. Now, same problem again, heard that familiar noise yesterday.



Friend advised that I look in the exhaust hose trap from that smaller black fan inside the unit (that t-junction down on the lower right), sure enough, sucker was full of water! I siphoned that all out of there and re-connected but still, no luck -- I did get it to attempt to fire up once again (the pilot) but now, when I turn the power back on, the inner fan runs, but I don't even hear the pilot attempting to light/click at all anymore.

Anything safe I can try to get some heat going for Christmas? I'd be most grateful.

Oh another question as well - Am I potentially doing harm to myself or the system to leave it running without the pilot lighting and heat flowing? Any gas risk by this happening? I don't smell gas but I assume it's flowing and without it being lit I'm not sure about the safety risk.

 

Oh and one extra comment - I'm not sure if this would have had any effect on why the igniter isn't even trying to start anymore, but a couple times I got lazy when I wanted to unplug a few things and shut off the unit using the red emergency shut off switch on the wall next to the unit. I've got it back on now, and am using the breaker to shut off power to the unit now when I am messing with it, but is it possible I have to reset something elsewhere since I had used that red emergency shutoff switch? Or a particular order I need to power/switch stuff back on? It's peculiar because yesterday, the Honeywell auto-ignite was at least trying to fire from the sound of it, today, it's not even trying at all.

 

The gas valve will not allow gas to pass thru unless certain criteria are met. If it isn't lit....no gas will be flowing.

It doesn't matter if you use the switch or breaker to turn off power. It also makes no difference in which order you turn them back on in.

Usually with a model number I can look at the wiring diagram and tell you how to troubleshoot. I'm not an HVAC tech but I work on this equipment a lot.

That small "fan" motor that starts at first is an exhaust draft inducer. You'll see a small plastic or rubber tube connecting that from the black motor to that round silver can called a pressure switch. This pressure switch is a safety device that will prevent operation of the furnace if correct venting air pressures are not detected. The furnace pressure switch is designed to sense the negative pressure created by the draft inducer motor at furnace start up and to shut down furnace ignition if proper differential air pressures and venting are not maintained.

I believe you have a condensing furnace and then there would be 2 lines to the pressure switch. These lines cant be clogged or the furnace wont light.

 

You have a "smart" valve gas valve and those things are notorious for failure.

 

Thank you guys so much for your replies.

One thing I learned was that the trap by the floor actually needed water in it, for resistance reasons, I was told to fill it back up, so I did.

I can now get the pilot to light again, after turning the unit on for about 1 minute, I hear the ignition (I assume that's the beige honeywell box) click and then while looking through the window, I see things light up in there, then the gas and some strong blue flame...This lasts all of 3 seconds before another much more pronounced click, and then the gas stops.

So it does sound like there's some sort of reason it's cutting it off, so I'll check the tubing to the pressure switch (thanks for the terminology, I had no idea what that tin can looking thing was) but it seems that's the reason it's shutting, so I can check its tubing and listen closely to see if that's the source of the clicks when it cuts the gas right off after it's clearly lit.

 

I actually managed to take a video of it, just on the off chance it might throw up a light bulb of what it might be so I can get the heat running today (VERY cold, we of course had snow last night).

You will have to cut and paste this into the browser and remove the spaces before and after the period, seems the form isn't liking my URL.

tinypic . com/player.php?v=2zhr6g9&s=6

If anyone has any ideas, though to me it's probably out of my hands and in need of a part and no new information.


This is a video taken via the view window. You'll hear the gas come on for about 3 seconds and then will hear the noise it makes as it shuts off.


This is probably not any new info, just confirming what you all already knew, but this is what it does. Sometimes it takes a couple minutes to do this after I fire it up, but I typically don't leave it on much longer after it fails, no idea if it retries.

 

It is time to call a pro.

 

I wanted to share more information to see if anyone can advise if this is now a fix I can do on my own, also in the hopes of helping others. A tech was out and disconnected the hose from the switch at the point marked with the blue arrow. As soon as he did, the gas turned back on and the house fan, all was well.

Reconnecting that hose kept things running so he thought it was going to stay working, but was still unsure if the part circled in yellow (pressure switch?) needs to be replaced. Part number on it is PPS10034-2278 but I can't seem to find one online so I imagine it's been replaced with a different part/number?

Sure enough, overnight, it stopped working again. The hose by the way runs into a plate marked with the orange arrow.

If I remove the hose at the spot marked in the blue arrow, what risks do I have in letting the heat run until the tech can come back out after the New Year holiday? Safe? Not safe? The heat turns on instantly when I disconnect that hose.

Also, if this is indeed the part marked in the yellow box, is that something I can just order and swap out myself? It looks like just two wires and a couple screws going into it.

Thanks all!

 

The pressure switch is a safety device that is there to insure that the furnace has proper combustion air to burn the gas. It should not be bypassed or disconnected.

Also, the furnace shouldn't work if it's disconnected.

Furthermore, a pressure switch that doesn't close is a fairly common symptom on a furnace that isn't working. 98% of the time the pressure switch is doing what it's supposed to and replacing it is a waste of time and money.

98% of the time, the reason the pressure switch wont work is that there is a defect in the furnace or venting system that is impariing the proper flow of combustion air and combustion gasses through the furnace.

Your repair sounds like he lacks the skills to correctly diagnose the problem, If he wants to check the pressure switch he should have used a manometer to determine whether the pressure was correct (which would indicate a bad pressure switch) or whether the pressure was low (indicating a combustion air problem.

What you probably have is a pressure that is low, but allowing intermittent operation of the furnace, which shuts off at other times when the pressure slips to an inadequate level. Had the repairman had the equipment and skill and motivation to measure the pressure and detect that marginal condition, he would have known there was a problem that needed to be identified and corrected.

It's all too common for repairman to encounter an intermittent problem and a furnace that is working when they arrive. The incompetent repairman says "Well, it's working fine NOW, call me when there's a problem."

The competent repairman looks for the weaknesses that are CAUSING the intermittent problem --- such as measuring the pressure being applied to the pressure switch.

The repairman also should know that the furnace shouldn't operate with the hose to the pressure switch disconnected. He should have investigated what is causing that. That COULD be a pressure switch that is sticking in the closed position, but guessing doesn't cut it.

A good many repaqir companies send out marginally competent repair people and have a supervisor or cometent repair person as a backup. I'd say you should be making a demand on the company to send a competent person out to repair your furnace NOW. They should be fixing your furnace NOW rather than accepting more business.

And frankly, if their repairman was as incompetent as hea appears to be, they should come out and do the job properly at no additional charge to you except for any parts that might be needed, in my opinion.

 

Thank you, I had posted this in another forum asking as well (just was desperate when I initially had no heat) and your response is right on the money to what the others are saying as well.

So now, I guess I'm really in a bind, though I may just switch companies altogether, as I don't want to get billed for a part I don't need, and it sounds like the pressure switch is fine.

You are correct by the way in that I just listed to the system turn on, gas fire up, and the house fan, from where I am sitting, with no intervention on my part at all. So that time, it worked, but later in the day, it might not.

So it sounds like you are dead on as far as it being a low pressure situation - Are there any checks I can do as a novice to check pressure? I don't want this guy (or anyone for that matter) to replace the pressure switch, or the smart valve (as earlier suggested in this post), if neither of those parts are the problem. I feel like I'll get stuck with a huge bill for parts that I didn't even need switched out to fix the problem.

 

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Guessing is not allowed!

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Yes. Wait until the furnace fails to light an see if the pressure switch is open.

You can wait until that happens. Better is to start the ignition process 20-30 times and hope that it fails to start properly so you can check the status of the pressure switch at that time.

All I'm doing is guessing that the symptoms suggest that the pressure switch is opening. What you need to do is confirm whether or not that is what is happening.

It could be a bad Smartvalve as suggested earlier. But if the pressure switch is opening, you confirm the theory I've suggested and rule out a Smartvalve problem, at least for the moment. If the pressure switch is staying closed, you rule out my theory and the Smartvalve theory is worth more investigation.

Does that make sense?

And you need to report the sequence of events that happens when the furnace FAILS TO LIGHT.

Fun, eh?

Intermittent problems are the bane of repairmen. You are probably beginning to understand why. Often they can be diagnosed, but they require persistance and expertise to do so. You supply the persistance and we'll supply the expertise if we can!

 

My Ducane sometimes started, sometimes not. In the morning, usually not. My thoughts were that the outside weather air pressure had something to do with it.

Anyway, I opened up the panel and examined the pressure switch. There is a clear, vinyl tube. I disconnected the tube. There was a small bug there. I got it out. Then I gently blew into the hose. I heard a clicking sound in the pressure switch. I connected the vinyl tube again and "VOILA!!!!!!"

The heater fired up immediately and all is well.