my furnace problems -- solved (pressure switch)

A few weeks ago, my furnace stopped working. After some time and $ later, it is now working fine and I would like to share my experience here so that it might help others with the same or similar problems.


The furnace is a Carrier/Bryant/Day Night model 397HAW036060. It is pretty old and was here when I moved into this house about 2 years ago. It had been working fine since I moved in until this first incident.

1st problem

When it first started, the inducer motor would start, the spark ignitor would continually spark and there would be a pilot flame however, the valve would not open and the burners would not light.
At this point, I had very little knowledge of furnaces as this was my first house and I had never had to deal with a furnace before. I called a repair guy. His methods of repair were not very good, as he began throwing parts at it. He replaced almost everything on the furnace until finding out what the problem was by calling someone else on his cell phone. This whole process took 10 days all of which time I did not have a working furnace and it was very cold outside. (I did have space heaters going).


1st solution:

He replaced the spark ignitor first (twice!), then the valve, then the circuit board, then the spark control module (sorry, if some of the terms are wrong), still nothing.
Well, there wasn't a whole lot left at this point, and he still only found the problem by calling the other person. And the bad part was the pressure switch. He figured this out by blowing on the hose attached to the switch at which time the valve would open and the burners would then light.

He then ordered a new pressure switch, however, all he could get was a universal one (even though I found the OEM replacement easily online and cheaper) and this is what he brought with him and installed. This worked for a while (more on this "2nd problem")

This guy was pretty lazy too, and he didn't even want to take all of the new parts out and replace my original parts that had nothing wrong with them. I told him that I was not going to pay for parts that I did not need in the first place, and he decided to leave them all in and only charged me for the pressure switch and labor (still a costly $323). Looking back now, had I have known the problem, I could have fixed it for half of that, however I do have a nearly rebuilt furnace now with all of those new parts (as well as all of my original working parts) and I also understand how it works and that helped me fix the second problem I had myself, and at no additional cost.


2nd problem

The repair work that was done lasted for about 2 or 3 weeks. As the time went on, it seemed the furnace was not keeping up with the thermostat. It would not keep the temperature that I had set. There would be times when the thermostat would call for heat and it would not kick on, however it did work at other times. This continued to get worse as the time went on, until one cold night it would not start at all. It wasn't doing anything, not inducer motor, no sparking... I inspected the furnace myself (now that I knew a little about it and was in no hurry to call that guy back or anyone else for that matter) and found that by tapping on the recently installed pressure switch (lightly), the furnace would start normally, get the house up to the temperature that it was set at, shut off, and then would not start again unless I tapped on it again.

2nd solution

Well, I was thinking about it all day while I was at work and then got home and messed with it some more. It seems that the universal pressure switch that was installed by the repairman was adjustable (found this out by seeing the super small allen wrench in the box that the part came in. It was unopened, and I knew that he did not adjust it. I looked over the instructions for the universal switch and it said that the switch had to be adjusted to the same pressure as the original, it also said that once the adjustment was made, to use some lock-tite to hold it into place.

At that point I took a closer look at how a pressure switch worked. When the air was pushed into the switch, it forced a plunger like plate forward inside the unit and a small metal point would then come into contact with the electrical portion of the switch and would make the circuit and it would work. By tapping on this, I was pushing it in just enough to make this circuit. I tested this by taking the tip of a very small screw driver and touching it to where the connection was made and it completed the circuit.

The old pressure switch did not say what it was set at and It wouldn't have done any good anyway as I did not have a manometer and could not test the pressure. I used the small allen wrench and made a very small turn on the adjustment screw (first marking with tiny drops of paint in case I had to turn it back to where it was). I figured that if I went too far, the furnace would not shut off as it would always be making contact, so as long as that wasn't the case, I would be all right. So that small adjustment I made, fixed my problem. The furnace is working great now.

My guess is that the vibrations from normal operation may have loosened this adjusting screw since it had been installed making for a worse and eventually no connection.
I have still not added lock-tite yet as I wanted to make sure this would work for a while first. This would prevent it from vibrating loose again. However, now that I know how to fix it, I'll just put it on the next time (if there is one), that this starts happening again.

I felt much better fixing this myself than calling someone again and spending more money.

While I know this may not be a problem or solution that many people have (as I did not find anything online about people with my similar problem when I was trying to figure this out), I wanted to post it here just in case it may help someone.

 

Well, jrich---


Sorry your repairman left a lot to be desired. Unfortunately, your own repair methods are no better, and could well be dangerous.

When a pressure switch opens and shuts off the burner, there are two basic things that could be wrong 1) the pressure switch is defective and needs to be replaced or 2) the pressure switch shut off because of a defect in the venting system that is creating a hazardous condition.

'Way too many repairman tend to jump to the conclusion that the pressure switch is bad and replace it, and indeed pressure switches CAN be bad. But about 90% of the time the pressure switch is opening because it is detecting a defect in the venting system which needs to be corrected for the furnace to operate safely and efficiently.

So here's my question for you: was your original pressure switch bad, or was it operating properly?

Answer: you don't know, but the odds are 90% that it was operating properly and detecting an improper operating condition THAT STILL EXISTS IN THE FURNACE.

I would guess that you repairman adjusted the new pressure switch so that it would keep the furnace on before he left. After two or three weeks that fix no longer worked reliably, perhaps because the underlying problem WAS GETTING WORSE. Now you have repeated the same bad practice of adjusting the pressure switch to close with the existing pressure, whether it is adquate for safe operation or not.


One of my pet theories is that the way to discriminate between competent and incompetent gas furnace repairman is to ask to see their manometer. If they don't have a manometer, they are incompetent and you send them packing.

If they HAVE a manometer, but it's new and has never been used, they get one point. If they have a manometer that's obviously been used and they have various lengths of tubing and fittings that allows it to be used, this is the repairman you want to hire, whether you have a problem that involves a manometer or not.

Now here's my question for you:

based on the method of identifying competence in a repairman described above, what level of competence do you have, and should you hire yourself to repair your furnace?

 

Wow, you sure assume a lot of things in your post. I admit you probably know more than me about furnace repair, but your post is full of problems.

Do YOU know that my pressure switch IS working properly and that the problem IS somewhere else.

Answer, NO.

"When a pressure switch opens and shuts off the burner, there are two basic things that could be wrong 1) the pressure switch is defective and needs to be replaced or 2) the pressure switch shut off because of a defect in the venting system that is creating a hazardous condition"


Did you not read my post, I believe it is you who are jumping to conclusions. The old switch would not turn on, the new switch would turn on (without any adjustments at all).


You say that you "would guess that the repairman adjusted the new switch before he left???

Again, did you read my post at all? He did NOT adjust it, he did not even open the wrench or apply lock tite to the adjusting screw, he just put it on straight out of the box.


The problem was clearly that he did not adjust the switch when he put it on. I hardly turned the screw at all to get it to work, less than a quarter of a turn (sorry I don't have a manometer, and I don't plan on getting one either)

I don't think that you understand the entire situation.

The second problem I had was NOT the same problem I was having when I first called the guy. At first, the pressure switch would not operate at all (BAD SWITCH) and all I got was the inducer fan started, followed by a constant clicking/sparking, with the pilot flame burning, while the furnace would never ignite.

After the new switch was installed and some time had passed, the second problem was the furnace would not do ANYTHING. As if the power switch on the furnace was turned off (it was not). No inducer fan, no clicking or sparking or pilot light (nothing).


If the new switch had the same problem as the old one, then I would agree with your assumption that the problem would most likely be elsewhere. However the problem was fixed with the new switch.

I do not claim to be a professional or necessarily a fully competant furnace repariman, however I feel that I am as good or better as the guy that I ended up getting, based on his performace.

Your criticism is hardly justified as you only know as little about my furnace, and my situation at this point as I do. You say, oh, it could be this or it could be that, but you could be wrong as well.

You sound like you are a certified repairman or something. You must get mad when normal people can fix their own furnace. This is the Do-it-Yourself board you know.

 

Hello rich,


So the old pressure switch wouldn't close. But were you applying the proper pressure on it at which it should have closed? You don't know.

As I said earlier, 90% of the time pressure switches don't close because of a defect with the furnace or venting system. They are staying open for a reason.


And just because a new pressure switch not calibrated to work with your furnace closed doesn't mean that the furnace is working properly. It really tells you nothing at all.

You can go back in recent weeks and find me giving advice to many, many people on getting their equipment working properly.

But the advice I gave to you is especially important, because there is no reason at all to suppose your furnace is working safely at this point. Indeed, the odds are about 9-1 that it is not.

I'm not at all surprised that you don't want to buy and learn how to properly use a manometer --- it takes a good deal of experience to be able to diagnose pressure switch problems accurately on gas furnaces anyway, and it's not something I'd recommend to you.

The test I posed earlier about evaluating the skills of a repairman based on their having and being able to use a manometer is really quite a good one. I'm not surprised that you don't want to draw the obvious conclusion.

 

I am not questioning your experience or knowledge here. Your advice can probably be very helpful to some, but is not very helpful to me, sorry.


"And just because a new pressure switch not calibrated to work with your furnace closed doesn't mean that the furnace is working properly. It really tells you nothing at all. "
How does this tell me nothing? It clearly tells me that the old switch was not working, while the new one was.

If you could tell me please, everything else aside, what would the symptoms be for a inproperly calibrated pressure switch (both over and under calibrated?)

"But the advice I gave to you is especially important"

What kind of advice did you give me anyway? I didn't see any except that you are somehow 90% sure that my furnace is not working right and that I need to get a manometer, despite being 2000 miles away from me, not ever seeing my furnace?

How can you be SO sure (other than quoting some odds to me) that my furnace is NOT working properly?

My furnace is now working the same way as it was before I had any problems at all. So, who is to say that the furnace has been working incorrectly for years then??? What are those odds?

I am done responding to this thread now so have a nice day and thanks for stopping by.

 

In the past you had a pressure switch which opened and shut off the furnace when the venting conditions were deemed unsafe by the manufacturer. Now you have an uncalibrated pressure switch. You have no idea at what pressure it will shut off, but it's pretty much a dead certainty that it wont shut off as specified by the manufacturer, since it's not calibrated. You understand? For all practical purposes you might as well remove the pressure switch and jumper the wires together.

At a minimum, you should install a new pressure switch as specified by the manufacturer for your furnace. If it works, then the furnace is presumably operating safely, and can be expected to shut off if it develops an unsafe condition.

If it doesn't work, or reverts to operating erratically, then you can bet you have a venting or furnace problem that still needs to be corrected.


Here's what a competent repairman would have done:

When they discovered that the pressure switch was opening, they would have installed their manometer on the furnace and determined whether 1) the pressure switch was bad since the proper pressure was present but the switch wasn't closing reliably. 2) The pressure switch was operating properly but opening because the furnace was plugged up in some way.

This test takes, oh, 10-15 minutes to do ----then you KNOW whether the pressure switch needs to be replaced or whether the furnace has a safety problem that needs to be corrected.

The marginally competent repairman who can't perform this kind of test will typically replace the pressure switch with the manufacturer's recommended replacement pressure switch and hope that that solves the problem. If it doesn't then he'll start looking for defects in the furnace or vent system to correct.

Unfortunately, you got an incompetent repairman who put a pressure switch that closes at an unknown pressure. That tells you nothing about whether the furnace is operating safely, and in the future you have a virtually 100% certainty that the pressure switch wont protect you against the unsafe conditions it is designed for.


At a minimum, I'm encouraging you to go the route of the marginally competent repairman rather than trusting the work of someone who has already proven themselves to be incompetent ---and dangerous, frankly.


Better is to look for a competent repairman to help you. I've already given you a way to test someone for that basic competence.

But perhaps you place greater trust in the methods and advice of someone you yourself have already determined to be incompetent. Having done my best to explain these things to you in several different ways, I have done my best to try to keep you from harms way.

Good luck. You probably need it.

 

All right. Lets' suppose you have a vent pipe that's partially plugged for some reasons ---- many things can cause that.

That would mean that the air flowing past the burners would be restricted, and not enough air would be present to burn the gasses properly. Result: large amounts of carbon monoxide and soot. Could be VERY large amounts of carbon monoxide, which might create safety problems in your home.

Suppose the inducer motor that circulates air through the furnace burns out, or doesn't turn at the proper speed. If the pressure switch is working properly, it won't switch on the furnace burners or the ignitor, so the furnace fails safe. Your uncalibrated pressure switch may still turn on the gas and ignitor which might cause a delayed ignition explosion in the furnace.

Lots of things could happen. The pressure switch is perhaps second only to the high temperature limit switch in protecting building occupants from Bad Things that could happen. To do it's job it is essential that it open and shut off the burners at the pressure specified by the manufacturer. Yours will no longer do that since it opens (if it opens at all) at an unknown pressure.

 

I am always surprised at the folks that will ask a question and then criticize a responsible, logical answer.

 

i am always surprised at the folks that will post a comment without reading the initial post. what i mean is.....THERE WAS NEVER A QUESTION TO BE ANSWERED, IT WAS A GUY THAT FIGURED OUT HIS PROBLEM AND WAS TRYING TO HELP OUT OTHERS WITH THE SAME ISSUES:bad poster:..........wheww.....ahem......thank you

 

I'm surprised that people that post an unsafe "fix" by either bypassing safety devices or substituting generic devices (which may or may not be equivalent to the original safety device) are surprised when PEOPLE WHO KNOW point out the mistake.

 

dazappa,

I think several other posters who understand how furnaces work would have posted if they found SP in error in his assessment. But he was correct. He DID read the first post. So did I. And I did not bother to respond, as SP had it correct.

Have you ever heard the expression about a person "knows just enough to be dangerous"? This expression came about because there are (many)people who think something seems easy enough, and they think they have the problem solved, or that they can fix something, without totally understanding all the ramifications involved.

 

Well, I know I said I was done responding to this, but after reading this I HAVE to make ONE MORE post.

First off, to respond to your statements:

Your responses are always assuming that everything else is the problem, basing this only on your knowledge of furnaces, past experiences,percentages, and only the info I gave in the original post.

The exhaust pipe WAS checked for obstruction by the original repairman. I also disconnected the pipe and looked for myself when the second problem occured. My burners are also in great shape. I was told this by the repairman (no matter how incompetant he may have been) and by looking at them myself. There is hardly any oxidation on them and they look like they almost look new except for the few areas where the flames constantly come into contact with and it is only a burnt color there, no rust or corrosion. Also the flames are burning cleanly and look the way any gas burner flames should look. You know only as little as I do about the condition of THIS furnace (even less in your case, as you can not see it).

Now, you can suppose all you want about the inducer motor burning out or whatever. I can tell by removing the hose from the inducer from the pressure switch that the furnace WILL NOT start. The gas valve will NOT open, the burners will NOT ignite . This means that YES, the switch does open (so you don't have to assume about that either). Also, when the hose is disconnected, the furnace behaves the same way as it was happening when I first called the repairman. This also tells me that the old pressure switch was indeed bad as it was NOT closing.

I am very confident that my furnace is working safely. It turns off and on when it is supposed to, keeps the temperature, will not work when there is no pressure applied to the switch, and you'll never believe this, but the CO2 detector hanging on a beam right in front of the furnace remains silent (before you say anything, YES, it is working properly). The same goes for 2 more CO2 detectors on the main level of the house. I am 0% concerned for my safety while this furnace is running.


When you responded to my question, you did not answer it. I don't know if you either misunderstood, or chose to ignore it and just type the same stuff you typed in your other posts, but here it is again.

"if you could tell me please, everything else aside, what would the symptoms be for a inproperly calibrated pressure switch (both over and under calibrated?)"


I asked that "everything else aside" , meaning if there is no blocked vents or inducer motor problems, etc....(that you seem to think HAS to be the problem) what would the symptoms be (what would the furnace do)? if all of that other stuff was working right and the ONLY thing that WAS wrong (even if you can't accept that) was that the pressure switch was over calibrated and/or if it was undercalibrated.

How about I try to answer it and you just tell me what you think of my answer ?

If the switch was OVER calibrated, the furnace would turn on when the thermostat called for heat (as it would with normal operation also), but the furnace would not shut off as the normal amount of pressure would be too much and the pressure switch would not open.

If the switch was UNDER calibrated, the switch would try to close, but would not have enough pressure to do so and the furnace would behave the same way as it did in my original post under "2nd problem".

You can (and did repeatedly) tell me that it COULD be something else, that COULD be causing the problem, but will not admit that this too COULD be the problem.

 

Do you have a 3-wire pressure switch that says by the electrical switch connections NO, NC, and C (or COM)? it sounds like you do, from the fact that rapping on it allowed the furnace to start.

Unless the new universal pressure switch said on it that in simple terms that as long as you could adjust the set screw so that the furnace comes on, that that means it is automatically adjusted right - that since it does NOT say that(otherwise you would have told us that) -then you are presuming - that just because you now got the furnace to work, that it must be right, or at least good enough.

When in fact it MAY be possible that you are in essence, bypassing (the safety feature of )the pressure switch that must be able to react to extreme small changes in vacuum.

The fact you said, in your "Second problem" that you believe the furnace would just keep running, if the pressure switch were not adjusted right, is not correct.

The pressure switch has nothing to do with how long the furnace stays running. And because you said that, then naturally, any professionals responding to you sees red flags, and wants to call your attention to perhaps an errancy in your reasoning, since you MAY not fully understand the workings. (For example, do you know why some pressure switches have 2 wires and some 3?)

I also read how you feel you have no other problem other than the pressure switch, since you went through this checklist of things proving you had good draft. But you did not mention all the things that can affect the proper drafting of the furnace.

......................

We really do try to help people here, so that not only can they perhaps merely screw in the right part, for example. But to call someone on perhaps a lack of complete understanding, so they do not fool themsleves and maybe get hurt, or worse. Maybe the language may seem rather blunt with some posters, but sometimes that is their style and has no reflection personally against you. The bottom line is we are all online here to help, or else we would not be doing this.

 

Everything I have researched indicates that:

1). Yes, you can get a furnace running again with a new universal pressure switch and

2). That doesn't mean the problem is fixed. If you don't do manometer testing, then you don't know if your pressure is correct. Especially with a more modern furnace, that is a critical bit of information.

It may or may not be worth it to you to invest in a manometer and learn how to use it. I don't use my multimeter very often, but when I need it, that is the only way I can get useful information about a circuit. The same applies to a manometer. It's not impossible to learn how to use it, but if you don't want to learn all the other facets of checking a furnace, then take the time to call a pro--and one who is licensed by the manufacturer.