Dear forum,
My heating system (Carrier Performance 96 58UVB) stopped working over the past few days. From the error code, it indicated that the flame rollout switch was tripped. I could reset the switch and get it back on, but only after 15-20 min, it trips again.

The box housing the igniter and the flame is hot to the touch after running for a 5-8 min. In comparison, another identical unit (58UVB) that heads up my basement was not as hot.

Comparing the two units, a notable difference is that the working heater (to heat my basement) turns on the blower shortly after the flame is on, but the one failed (to heat up my first floor) only has the blower on intermittently or never turn on.

I suspect that if the blower is not on, then the heat will build up in the igniter box, and trip the rollout switch.

I saw some videos talking about replacing the blower capacitor, is this what you would recommend or there might be other sensors that are not working?

thanks

 

from the below link, you can see two photos of the furnace.

https://photos.app.goo.gl/YT1UkJE2zwAD71c78

I just checked the blower by opening the bottom panel, but I don't see any visible capacitors mounted on the accessible side. anyone know if this model has a capacitor?

Update: I searched on the Internet, it looks like the blower motor is an ECM motor, so, it is not supposed to have a capacitor. In such case, I am wondering what other components can go bad if the blower does not turn on (even after a long time) after the flame is on?

 

I would first inspect for signs that the heat exchanger is cracked or rusted through.

 

ECM motors are nice in that they are multi/variable speed and more efficient than the older PSC motors. The downside is that if they fail (not an uncommon condition), they are VERY expensive to replace. A replacement motor typically costs over $1,000, not including installation. Often, when an ECM motor fails, it's the electronics module bolted to the back of the motor. Depending what's wrong with the module, it may be possible to repair it. Here is a thread that discusses the possibility of repairing the module:
https://www.doityourself.com/forum/a...ble-motor.html

Note that there are ECM testers that will test the motor assembly (motor + module) and determine whether the motor assembly is the problem, or if the problem is with the electronics board in the furnace. However, you would need to contact an HVAC company to have the motor tested (if they have a tester).

 

thank you Pilot Dane and Bob14525 for your quick replies.

For Pilot Dane's comment, I don't want to rule out heat exchanger cracks (the heater is about 10-12 yrs old), but making an assessment will require taking the heater apart completely. But from what I can see, the blower motor fails to kick in while the burner is blowing flames could explain why the rollout switch is tripped - because the heat won't be delivered to room timely and build up in the unit.

Right now, my first line of suspicion is that there is some sensor that tells the blower to start is not functioning properly, but I don't know the name/type of the sensor in order for me to read more or locate it. does anyone know what kind of sensor is responsible for starting the blower? does this have anything to do with my thermostat (google Nest)?

For Bob14525 I also pray that my blower motor is not bad - it does kick-in sporadically, and when it starts, it runs fine.

 

There are multiple limit switches on your furnace.
The flame rollout switch is not normally affected by the main blower.
It's typically tripped by a flue problem/clog, problem draft inducer, over firing/gas pressure issue and possibly a cracked heat exchanger.

 

@PJmax, if the main blower for some reason does not turn on, would that ultimately trip the rollout switch?

when the faulty furnace turn on, I do hear some grinding noise from the inducer motor (which does not appear on the other working unit), but only last for 3-4 seconds. Then inducer motor seems to spin normally without noise.

 

"... if the main blower for some reason does not turn on, would that ultimately trip the rollout switch?"
The flame rollout switch pretty much just senses flame where it should not be. If it is tripping something is wrong. I have never had one trip due to an air handler fan issue.

Watch he burners when the furnace is running. Do you see nothing but big blue flame going through the heat exchanger pipes or is there also yellow or orange? Do you see any flames getting blow out of the heat exchanger?

 

I did see something, and it is getting progressively worse.

Yesterday, when the rollout switch initially get tripped, when I turn on the heater, I see mostly blue flames, but in each flame, there is a small yellow dot - a technician who came to diagnose the problem said it might be some insulation material in the flame (the tech essentially did nothing, after 20 min he left, the sensor tripped again ).

https://photos.app.goo.gl/sKB4yYV5pV4jHywK6

Today, when I turn the heater on, the inducer motor started loud grinding noise and it does not go away. After burning the heater for a couple of min, I took this photo (I turned off the unit immediately)

https://photos.app.goo.gl/CyFrJZdK7UAzTxCX7

clearly there is something inside that is burning hot. I am wondering if a failed inducer motor can cause this? is it worthwhile to replace the inducer motor and see if can work again or the heat exchanger is beyond saving now?

here is a video I took today shortly after the burner turned on
https://photos.app.goo.gl/PvWZ5fzq5fLNt5ui7

 

The furnace will not run unless the inducer is running. If you see some rubber hoses inside the unit they are connected to the inducer motor plenum and a pressure switch to sense when it's moving enough air. The controller looks to make sure the air pressure is good (indicating that the inducer fan is running AND working) and only then does it allow a flame. Even if the inducer motor keeps turning but it's fan falls off somehow the air pressure sensor immediately sees that there isn't a draft in the combustion chamber and shuts down the flame.

Have you checked the exhaust path to make sure nothing is blocking it?

 

That furnace is part of a class action lawsuit for faulty heat exchangers.

http://hipspro.com/pubs/Furnace-clas...led_notice.pdf

The symptoms you describe are indicative of a failing secondary.
When this happens the tech will note an elevated level of CO in the exhaust when performing a combustion analysis. Advanced failure will produce an irritating odor from the exhaust.
There is no quick fix for this. You replace the heat exchanger which is major surgery, or replace the furnace.

 

Just watched your video, definitely looks like a failed secondary heat exchanger to me. The flame on the burner on the left in your video appears to be rolling out and not being correctly pulled into the primary heat exchanger anymore. There are other possible causes but not likely on that furnace. Don’t keep resetting it, it’s probably producing tremendous amount of carbon monoxide, also if that rollout switch doesn’t open and shut the burners off then it quickly becomes a fire hazard. I’ve seen them melt and burn the combustion air inlet pipe near the burners. Time for a service tech on site to confirm, preferably one with a combustion analyzer, but carrier will still approve the warranty with just (CO) readings at the flue/vent I believe.

 

@Furnace Man, thanks for your comments.

I think I know part of the problem, but the furnace still does not function fully. Here is the the detail

As I mentioned above, the inducer motor started making noise during the period - initially only a few seconds at the start, but then progressively getting longer, and the video I showed with roll-out flame was recorded during the first time when the inducer motor continues the noise - you can hear the noise in the video.

I removed the inducer motor and open it up, I found that it was caused by bad mounting - one of the 3 mounting screws some how was lost. I remounted/leveled the inducer motor, and put it back, now it no longer makes the grinding noise, and the flame do not rollout as badly as it showed in the video.

However, this still does not fix the problem that the rollout switch still get tripped - not after burning for a few min, but after hours.

again, comparing another working unit of the same model (heating my basement), a big difference is that this faulty unit does not start the blower motor nearly as frequently as the other one. All the vents have very little air flow. It does start occasionally, but not as immediately or frequently as the working unit.

The blower motor is an ECM motor. see a photo in the below link - does this mean I have a bad sensor? or the control board that tell the motor to start is not working properly? any pointer on where to look at would be greatly appreciated!

https://photos.google.com/share/AF1Q...ZNUG5DYmFabHhB

 

roughneck77 , thanks for the link and information about the class lawsuit - I will read more about this. I will also call Carrier on whether my unit has the extended warranty on the secondary exchanger. If this was indeed the cause, I guess nothing I can fix on my own.

 

A combustion analysis should be run either way to check the health of the heat exchanger. This should be the first step.

 

The secondary is most likely bad.

It is not worth replacing under warranty, unless the entire cost is covered by carrier's labor coverage.
The inducer assembly, blower motor and main circuit board are extremely expensive in this furnace.

It is a real shame because beyond bad secondary hxt and super expensive parts - it is an excellent, good quality furnace.

You can get money towards a replacement carrier that doesn't have this problem. Talk to a carrier dealer.

I would recommend the carrier 59tn6 infinity 2-stage if you replace with another carrier.
It is the closest to what you have with the same type of main blower motor.

The 59tp6 has a inferior main blower motor that won't give proper airflow in heating mode if your ducts are a little undersized.