Carrier Furnace Won't Start -- Will Start Manually

I have a Carrier Gas Furnace - 58MSA. About 12 years old.

Last year I had the ventor motor replaced and something else several months before that. I don't remember what, exactly, but it was just as expensive.

I've also cleaned the flame sensor.

This started happening a few weeks ago, but it's fairly consistent now. The furnace won't turn on. The thermostat upstairs says it should be on, but it's not. I can flip the electrical switch beside the furnace off and back on, and it will fire up, reach temp, and turn off for good. I have to do that every time I want the furnace on.

I've seen error codes 13 and 14.

I replaced the filter (we have two washables we rotate), I didn't see any blockage in the pipes outside (blows fairly strong out there when it's on). When the furnace does turn on, the air flow seems very weak, but that could just be me being paranoid.

Any ideas? I'm going to replace the thermostat tomorrow just in case. It's just a Honeywell digital one. Other than that, I'm at a loss. I'm comfortable replacing parts that don't involve either 1) messing with the gas lines or 2) taking a whole lot of stuff apart to get at it. I'd rather not drop another $500 on this aging thing.

 

Guessing by replacing the thermostat is a waste of time and money.


Take the cover off the burner compartment of the furnace.

Observe the sequence of events that occurs at the furnace when you turn up the thermostat and post that sequence of events in order and in detail.

Look for any diagnostic lights on the ignition control and post the sequence of flashing lights.

 

This legend tells you what to check. When you cycle the furnace power all you are doing is resetting the control board that is in lockout. IT IS NOT YOUR THERMOSTAT!

 

Thanks for the replies! The furnace seems to have been working fine all night. The only difference is that I cranked it up to 73, and it seems to have been able to maintain that. Normally it's set to 69 or 70. Could the higher temp be something?

In any event, I've got some more detailed information for you:

I went down and flipped the electrical switch off and on to observe (the furnace was on at the time so I gave it a minute to spin down):

- Fan comes on (I think it's the fan--whatever is in the bottom-most compartment) for 60 seconds. LED flashes code 12.
- Fan turns off after 60 seconds
- Ventor motor starts to spin with a solid LED light. The motor gives off a slight whir sound. It's brand new, mind. Anything I can do to lessen that noise? It's noticeable if you're down there when the furnace turns on. Anyway, motor spins for 20 seconds or so.
- Orange flame in the burner compartment for a few seconds. Blue for a split second, shuts off - LED code 34.
- The above repeats after a few seconds. Then it goes again, but the blue flames stay lit the third time.

So with my limited knowledge, flame sensor? I already cleaned that thing last year. Also, since this may help, when we had the furnace cleaned last winter, the guy said there was a lot of dust in the burner compartment itself, and he said it could have been pushed deeper inside as part of the cleaning. Then, it wouldn't turn on after he was finished with his work. He sprayed a bit more air in there, and then it worked fine for a bit, until it didn't.

I had to have someone come out shortly after that, and he blew some air into a rubber hose that was attached to the pressure switch. It fixed it.

 

The diagnostic code is indicating that the ignition control isn't detecting that the burner flames are being detected.


So yes, try cleaning the flame sensor.


Do you have a good multimeter that will read down to microamps (1 million microamps= 1 amp)

 

I've already cleaned the flame sensor last season, and it was completely shiny already. I'd much rather replace it this time. Where would I find one?

And I don't have a multimeter. Could I find a sufficient one for around $30?

 

Clean the flame sensor. It takes fives minutes, costs nothing and needs to be done annually as regular maintenance in any case.

Then use a multimeter to measure the AC voltage being applied to the flame sensor when the HSI is heating up and report that here.


A cheap multimeter is probably not going to be sensitive enough to measure the flame sensor current, but do the above things first.

 

Cleaning the face of the burners that is exposed to the flame and all ground connections would also help flame rectification.

Avoid the area around the ignitor, it is easily broken.

 

How would I go about doing that?

 

you would remove the burners. If you do not feel confident in your mechanical skills to remove the burners I would suggest calling a Pro. I will say that removing the burners on that furnace can be a pain as you have to remove the gas valve and manifold assembly to do so. Reclean the flame sensor while you are at it.

 

In other words, am I messing with gas lines? I'm comfortable with anything that doesn't involve that.

 

Yes. It would involve gas lines.

 

An AC voltage is applied to the flame sensor. If a flame engulfs the flame sensor, a small DC current will flow to any steel on the burners or heat exchanger the flame touches. Detecting the DC current is how the ignition control verifies that the flame is lit.

It's possible I suppose for so much of the steel to be coated with oxides that the current can't find a ground, but I've never observed that myself.

Far more common is that the FLAME SENSOR IS COATED WITH OXIDES.

Or that THE IGNITION CONTROL ISN'T APPLYING THE AC VOLTAGE TO THE FLAME SENSOR because of a defect in the ignition control.


If you want to clean burners, help yourself.

If you want to solve the problem, investigate the issues that are likely causes of the problem.

 

I usually see a greater increase in the microamp reading by cleaning the grounds and burner face than cleaning even the greenest flame sensor when I take the time to measure before and after cleaning.

This is not a common lockout around here. I'm confident that Seattle has seviced more flame sensor lockouts than I have and that furnace would be tough to clean.

I usually only measure after cleaning and see between 3 and 5 microamps dc.
The manual states that the OEM board requires at least .5 microamps dc.

 

Hello Houston,


Well, our reader is reluctant to even clean a flame sensor, let alone disassemble and clean the burners.

My method was to encourage him to clean the flame sensor since that is easy to do and might get things working. And in any case, it is maintenance that should be done before doing anything else.

Step two would be to check to see if the ignition control is providing the needed AC voltage. That can be done with a cheap multimeter, while measuring the microamps requires a more sensitive multimeter than he apparently has.

I'm thinking: do what you can with the skills, instruments and motivation that someone appears to have and see if that is enough to solve the problem. If not, you may need to call a serviceman.

 

The only reason I'm reluctant to clean the flame sensor is because I've done it twice in the past year already. It doesn't seem to be the problem. The symptoms are always the same (furnace stops turning on at all or intermittently. lockout code). Last time it was a weekend and I kept manually resetting the furnace so it would turn on, and that apparently broke the ventor motor (loud clicking noise from it when it turned on). That was over $600 to fix. And it didn't even address the original problem. After clearing out the rubber tube attached to the pressure switch, it seemed to be fixed back then.

Now, a year later, the symptoms return. If it is the flame sensor, I'd much rather spend the $10-$20 and replace it completely. Because it simply can't be dirty. I've cleaned it twice to a shiny, shiny finish. These things shouldn't need to be cleaned every year, right? If the flame sensor is the problem, it needs to be replaced. I just don't know where to find one.

And it's a royal pain in the ass to get in and out without removing the vendor motor. It takes about 30 minutes, not 5. Unless there's an easier way you can tell me about. It's the act of actually getting it in and out that takes time. It's extremely cramped back there. Imagine loosening and tightening a screw in a 1 inch space around a corner, from below. Without any line of sight. And trying not to break the little circuit board piece back there.

Does the fact that the symptoms are intermittent not point to anything more directly? The furnace has been working fine the past day or two, for example. And one time when I watched it start up, it took three times to finally stay lit. What would that indicate?

 

That would indicate a low or no flame signal. CLEAN THE FLAME SENSOR! it takes a little bit of work to clean it, yes. However with stubby or 12" long 1/4" nut driver it is not that hard.

 

Would it not make much more sense to replace the flame sensor that looks perfectly clean but has been giving me these problems? If it's only $10, I'd much rather do that.

Why isn't that a better option? What am I missing?

 

a flame sensor is a piece of steel. Nothing special about it. Straight flame sensors like yours dont fail unless the porcelain cracks. They do, however, get dirty and they DO need cleaned annualy as normal routine regular maintenance. A dirty flame sensor is the #1 reason for a furnace to lockout.

 

http://www.docs.hvacpartners.com/idc.../58msa-4sm.pdf

page 15 of the manual may help...

 

I apologize.... SP got me off on the flame sensor tangent. A flame sensor has nothing to do with a code 33 limit opening. You need to check the temp rise Vs. the rating plate to make sure that is in spec.

The main limit is square or rectangular and has 2 wire connections going to it.

Are all your vents open? Try running it without the filter or put a cheap throwaway in. Washable filter never get completely clean

 

Haven't seen a code 33 on it. It was showing 12 then 34.

I'll give the flame sensor another cleaning if you don't think replacing it is a good idea.

Edit: And all vents are fully open. The washable filter in there now is fairly new as well.

 

a code 13 only comes after a code 33 has been present for more than 3 minutes. You originally stated Now you are saying Code 12 is normal after turning furnace power off and then back on while the thermostat is calling for heat. Code 34 is an ignition proving failure code and relates to the flame sensor circuit.

What are you cleaning your flame sensor with? What ever it is, make sure you wipe it off (after cleaning) with a clean cloth.

 

I thought for sure it was 13 and 14, but every time it has failed to start and I've checked, it's code 34. I may have mis-read the codes the first time. Or maybe it was putting out 13 and 14. Either way, it's been 34 ever since.

I'll report back when I have results from cleaning the sensor again. Thanks again, everyone!

 

I am having the same problem with my Carrier heater. Just wondering if Nswyers has found the root cause. Thanks

 

i just figured out a series of issues with my furnace as well some were the same signs you were having mine was a result of a bad ground to check this put your test probes on the R(red) termanal where your tstat wires in and the other on the ground anywhere will work as long as its a clean metal surface of the furnace housing im assuming your furnace should be 24v it should read around 27v if its less find your grounds its usually the green wire attached somewhere around the flame box and clean the termonal good luck

 

I followed dog1031suggestion and clean off the ground screw and the mounting area and seem to do the trick. It has been 2 weeks and still come back on every time. Thanks dog1031.