A learning experience that isn't over. Furnace issues.


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Old 11-03-09, 07:49 AM
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A learning experience that isn't over. Furnace issues.

Hi.

A brief history. Bought a house about 2 years ago (roughly 5 years old) had it inspected and was given the thumbs up on everything but a bad GFI outside.

The first winter came and went with no issues, everyone was nice and warm.

For the first summer, I had a gas line run outside for a BBQ. During that process the tech who was helping me took the cover off the furnace because he saw a little rust near the bottom of it. We discovered one of the drainage hoses had been disconnected probably because it had a kink in it. (So much for the inspection!) Needless to say the tech bent the kink out as best he could and reattached it. He told me that I probably would want to rerun that hose as its not the best.

So like any other lazy home owner, I filed that in the back of my mind and never got around to replacing it. We enjoyed another warm winter, and it was forgotten about.

Fast forward to a couple of weeks ago and we had the first cold snap of the up coming winter. The furnace behaved and ran fine.... for a couple of days. It then stopped.

I took the panel off the front, and saw three fllashing lights on the control board. I saw that this meant "Pressure switch Open NC. I proceeded to jump on google and discovered this forum.

Subsequently I have been reading a lot of threads and trying various things, all while building my confidence and knowledge on what used to be very intimidating to me.

The first evening, I took off all the hoses, discovered a water blockage between the pressure switch and the induction motor. I got the diagnostics lights to go away and got the induction motor to fire up and run. Eventually the furnace kicked in and ran most of the night but died again.

The next day I tried to reproduce what I had did the night before. Nothing would work. I then proceeded to do more research online, try something.... do a little more research... try something else. I increased my confidence to the point that I taken everything I could off hoses/vents/induction motor/pressure switch... everything seems to check out fine.

I was at the brink of frustration and ready to call an expert when the furnace started running again. Coincidentally it started at roughly the same time the night before. Programmable thermostat! Didn't make sense to me, as the thermostat seemed to be acting fine. I could use it to start the ignition sequence. I could turn the blower fan on and off.... but I changed the batteries in it anyways. Problem disappeared all was good. Behaved for a week.

It then got warm for quite a few days, and I was hoping there was going to be no more issues. I replaced the bent hose, used a 90 degree pipe so there was no stress on it at all... blew out the trap at the bottom (although I can't open it?) and waited for it to get cold again. It did.

Yesterday I came home to a cold house. My induction motor just keeps running, and I can't get the furnace to start up. There is no water blockage and I drained what little there was in the system.

My thought is to buy a new thermostat to see if it has been the source of my troubles (other than drainage) but wanted to post here before I did. I don't know a lot about thermostats or the control board, but I always thought the signal was on or off. Does a thermostat have that much control to begin the sequence but not finish it?

The led on the control board says all is good.

Its a Clare furnace, about 7 years old now.

Any other suggustions and possibilities would also be greatly appreciated. Its a pride thing now.

On a side note, I am addicted to this forum now.

Jason
 
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Old 11-03-09, 08:08 AM
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Generally speaking, the inducer motor wont run unless the thermostat is calling for heat.


You need to identify how far along in the sequence of operation the furnace gets before it fails to get further.


Take the cover off the burner compartment so you can observe the controls and the furnace rating plate.

Turn the thermostat down, which should shut the furnace off.


Then turn the thermostat up, which would start the ignition sequence. Report the series of events that occur. You may need to do that several times before you observe all the details of what happens.
 
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Old 11-03-09, 08:26 AM
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That is kind of what I thought, which is why I never bothered with the Thermostat in the begining. I then got confused by the fact that it had started on its own at roughly the same time of the evening and even more by it running fine for a few days after switching the batteries.

I won't be able to play more until after work. I'll let you know what is happening.

Thanks

Jason
 
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Old 11-03-09, 09:23 AM
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It's quite common to be diverted by various things that you see when you don't have a systematic way to evaluate what is wrong.

Understanding the sequence of operation of your furnace is a powerful way to identify a problem that is preventing the furnace from operating.
 
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Old 11-03-09, 05:15 PM
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Since you know that your inducer is running,.... you then need to check that you have both incoming 24 AC volts to the pressure switch, and outgoing 24 AC volts. Ignition cannot occur until that happens.

All the other stuff you said could be a coincidence. Only after say 5 -10 test runs doing the same stuff after you replicated what you did, could you probably say no coincidence.

IF say your pressure switch IS allowing the passage of 24 volt juice, as it should be, - then it could be an ignition process that is marginal because of either a going-bad ignitor or control board.

If your pressure switch is not staying closed, while the inducer runs, then you could have varius other problems besides the condensate backup issue. Like blocked venting, plugged up furnace, plugged up inducer fan housing nipple that the 1/4 inch vacuum tube plugs into, bad heat exchanger, bad pressure switch itself - to name some.
 
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Old 11-04-09, 08:07 AM
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Hi.

There was voltage at both sides of the pressure switch.

I thought before I tried taking the burner compartment apart (it is sealed by multiple lag screws located in spots that would be a pain in the ass to access) I would just try my hunch at replacing the thermostat. I figured I could take it back if I was wrong, and it was cold in the house so I was desperate. It fired up right away after switching it, so I switched back to the old one. I once again got just the induction motor running again. Obviously I switched it back and have heat now.

That makes no sense to me. Time will tell, but is that possible, or do you think its still some other intermittent issue?

On a side note, I was discussing my problems at work. Another coworker of mine has simular drainage problems. Is the trap that the water lines merge at before leaving the furnace area by one pipe anything more than a sort of funnel? He thinks its plugged, but says it is sealed.

Thanks again for the help.

Jason
 
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Old 11-04-09, 10:11 AM
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Originally Posted by diseased-dog
Hi.


Yesterday I came home to a cold house. My induction motor just keeps running, and I can't get the furnace to start up. There is no water blockage and I drained what little there was in the system.


The inducer motor isn't going to be running unless the thermostat is calling for heat. That's the way the sequence of operation on most furnaces works.

So I would say it's very unlikely that the problem was the thermostat, at least while you were performing this test.


Of course, it might have been that at other times the furnace wasn't turning on because at that time the furnace was on a setback and not calling for heat.


I've already suggested that a scattered approach of looking at things in a random way is a poor way of figuring out what the problem is, and your description of your methods is a perfect example of that.

Since it's entirely possible that the problem will recur again, my suggestion is to take the time to carefully observe the sequence of operations that happen to produce heat.

I'd take notes on that and leave them in a notebook at the furnace. When you have a problem again, you will have the experience of having observed the furnace when it was working properly, and can compare that with what's happening when it isn't working properly.
 
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Old 11-04-09, 11:14 AM
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I wouldn't say a scattered approach, just an uneducated one. My deductions might have taken me down the wrong path, but atleast I am learning.

I'll take the time to access the burner compartment and follow the sequence with notes like you suggest. Especially since I am getting the feeling you think the problem is going to reemerge.

I am still having drainage problems from the "trap?" on. I cut the pipe from the trap to the drain so I could take it out of the furnace and look at it. It is sealed, and I applied some pressure to it and blew some crap out of it, but the thing still doesn't drain freely.

Is it meant to have a certain amount of water in it?

Also, does it serve any other purpose than merging the two drainage lines into one? Can I replace it with a y adaptor?

Jason

Thanks for the patience by the way.
 
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Old 11-04-09, 12:48 PM
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There's probably no need to open up the sealed combustion system, at this point, anyway. I presume there is a viewing port where you can observe the burners?
 
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Old 11-04-09, 12:51 PM
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I'm not familiar with you furnace in particular. But in general, the drain system needs to work freely, and drain traps can get clogged with gunk. If you can't clean it out to work freely, replace it with a replacement specified by the manufacturer.
 
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Old 11-04-09, 04:29 PM
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Hi.

So I temporarily rerouted the exit drain with some clear tubing so that I can see that everything is draining properly. I am going to try and track down a new trap, because I am still not happy with what is getting through. How much water should be generated while running? I know it would vary by your environment, but is generating too much moisture a sign of something?

There is a small distorted view window in the combustion system, but short of seeing spark and flame, you really can't tell much else.

Jason
 
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Old 11-04-09, 04:47 PM
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Does the pressure switch continue to show voltage to both sides even if the fire never comes on, or goes out? This is very important.

Breifly explain again what the furnace does or doesn't do, after the inducer runs, and you have that votlage at the pressure switch. We need to know conclusively if the fact you have power that at the pressure switch, that it is there when the furnace both fires and doesn't fire(of course with a call for heat in both cases). IF the pressure switch always has power to both sides, even when there is not fire, THEN you can rule out furnace condensate drain issues making the furnace not work. But we have to be certain that the pressure switch really keeps letting 24 volt power through it, even when no fire.
 
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Old 11-05-09, 05:32 PM
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Well, it died again. Once again there was a lot of water in the system.

I tried briefly last night to see if I could get it to run without the drainage trap and with the clear tube I installed, I witnessed the oddest behaviour. (Atleast odd to me) Moisture in the tube was being pulled back into the furnace. Is that normal?

With the system drained, I am back to where the inductor motor just runs. In that situation there is 26.9 volts to the pressure switch and nothing out of it.

I am going to go disconnect all the hoses and see if I can get it running again. I will check the voltage again once its running.

Jason
 
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Old 11-05-09, 06:28 PM
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Hi.

Got it running again. It seems moisture getting into the pressure switch has something to do with it.

I do not get any voltage readings at all once the furnace is running though.

Is that right?

With the lights out I can see better into the combustion chamber. Everything there seems to appear as its normal (no delays in ignition or anything)

Jason
 
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Old 11-05-09, 06:57 PM
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Moist air really shouldn't be able to even get into the pressure switch since the vacuum is pulling away from it and toward the inducer. But, have you pulled off the 1/4 inch vacuum tubing and it has water in it?

As far as the condensate being pulled back into the furnace goes - I am not an expert on the engineering aspect - but I have seen this myself. If the furnace runs fine, and the water makes it's way to the drain, then all may be alright. Check and see. If this suction prevented water from draining, that be another issue.

You might wonder how it is possible for the water to drain, if it is being drawn toward the furnace, rather than heading toward the drain. What will happen is - so much water will be pulled backwards, but then the suction is not strong enough to pull it, let alone even hold onto it all - and then the excess water breaks free and goes to the trap and drain. That's my take on this anyway.
 
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Old 11-05-09, 07:46 PM
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Hi.

In order to get it running I do have to take the clear vacuum lines off the pressure switch and get the moisture out of it. I also disconnect the switch and shake it a bit as moisture does get inside.

I rigged up some tubing to the drain trap and connected it to a faucet. I was able to blow out a bunch of crap that was built up inside of it. It now seems to be draining better.

I think my issue may have been the trap causing water to back up into the vacuum lines on the switch. But who knows. Tomorrow I may be trying to figure it out again. I can visually see water draining now, which I did not witness yesterday.

If this does turn out to be the case, should I be replacing the pressure switch? I had read something about them being dangerous if they become inaccurate. Is it not having any voltage readings when the furnace is up and running normal?

Jason

Thanks for all the help guys.
 
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Old 11-06-09, 08:32 AM
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Originally Posted by diseased-dog
If this does turn out to be the case, should I be replacing the pressure switch? I had read something about them being dangerous if they become inaccurate.
It's possible, yes. This is the reason why they invented the 3-wire pressure switch, as opposed to the older 2-wire variety. In theory, if the plunger got corroded and no longer could freely move back and forth, and got stuck in the closed(or working) position, then you'd lose the safety feature of how the PS can protest you in the event a of a furnace malfunction. It is for that reason that they came up with the 3-wire pressure switch. With that system, for every furnace cycle, the PS has to prove to the furnace that the plunger can move. The furnace will not start until the plunger moves back to the original position. And then once it starts up, the PS plunger has to move the other direction to again prove it works that direction in order to get ignition.

Is it not having any voltage readings when the furnace is up and running normal?

It is normal, IF you are checking voltage ACROSS the two PS terminals. You are testing in series. The readings you get will be backwards from your thinking. When the pressure switch is turned off(open circuit), you will get a 24v reading. When it is turned on(closed circuit), you won't. It has to do with how testing in series behaves when it goes through a resistor. Your test meter is a resitor. When you test in series, the voltage takes the easiest path to ground, which is through the pressure switch, rather than the test meter. But when the pressure switch is turned off(open circuit), the ONLY way it can get to ground is thru the test meter, so therefore you get a reading then. That is why I like to always test between a hot terminal and ground, rather than testing in series. The logic is more quickly understood, when you test that way.

Thanks for all the help guys.
Hopefully this helps - and your problems get behind you. But note this: When you blow out the trap, you will get resitance in your blowing, naturally, by virtue of trying to blast clear the weight of the water in the trap. The water is supposed to be in the trap for one thing to prevent exhaust gases from escaping. But I guess time will tell if this cured your problem. If water now drains, and before it wasn't, then perhaps that was your problem.
 
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Old 11-08-09, 06:26 PM
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Just wanted to let you know everything has been running fine for a few days now. It had to be the drainage issue.

Thanks for all the help.

Jason
 
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Old 11-08-09, 06:46 PM
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