Bryant Furnace Limit Circuit Fault - 33

Users who are viewing this thread

gcc

Member
Messages
33
Reaction score
0
Points
6
Location
Tampa, FL
Hi all,

Hoping you can help with an issue. In December our Bryant furnace had the Limit Circuit Fault error - 33.

Called A/C company and they replaced the control board and motor. After they replaced the parts they tested it with the door off/switch taped and it worked. It's Florida, so running the heat is rare down here. Thought it was fixed.

Last night it was cold. Turns out, the same issue is happening. Fault 33. Heat kicks on then the whole system shuts off after a few minutes and the LED displays the code. I tested all of the switches mentioned in the fault description and they all seem to be fine. The filters are not too old and don't look bad. The control board and blower motor are new. I will say the exhaust vent gets super hot.

Here is where things get weird. I took the door off and taped the switch again and the heater worked fine. It was going for a good 20 minutes. I realize it has access to a lot more air coming in that way. Then I put the door back on and before I could even finish putting the screws back in the system shut off. The other thing I noticed was that there is a 4 inch exhaust vent hose coming out of the furnace into the attic - but - in the attic it converts to a 3 inch vent hose for the remainder of the way straight out the top of the roof (about 8 feet).

So - does opening the door help force air out the exhaust? I'm not sure where to go from here. DO I need cheaper/see through filters? DO I need to change out the vent pipe in the attic? Or do either of those matter?

Thanks,
Greg
 

breplum

Member
Messages
734
Reaction score
258
Points
63
Location
San Francisco Bay Area
Sounds like not enough air flowing, impaired return air somewhere, or undersized (which is somewhat rare on systems with A/C b/c A/C runs on high speed and needs good sizing to prevent coil freeze up).
Yes, remove the filter to see if it impacts situation.
I would definitely check the exhaust vent specs as well. I don't recall any Bryant 80+AFUE furnaces that allow 3".
I've encountered things blocking vents: Paper wasp nests, dead rodents ...
 

WorthFlorida

The wife is still training me.
Messages
4,645
Reaction score
699
Points
113
Location
Orlando, Florida
Surprised you have a gas furnace in Florida since our heating needs are short except this week. I know nothing about this furnace, however it sounds the there is not enough air supply and things seems to work when the door is removed that allows more air. One clue is you mentioned "exhaust vents" get very hot. Another possibility is there is not enough air flowing over the plenum to absorb the heat and allowing the exhaust temps to get too high.

From a google search.
Furnaces have a safety component that will detect when a flame rollout occurs — the flame rollout switch. This switch stops the supply of gas to the furnace if the temperature outside the combustion chamber exceeds a certain level.

So what is this 4" vent. Is it the chimney? 3" would never be used for a furnace exhaust vent. It could be a fresh air supply. It appears there isn't enough draft and the plenum is getting too hot. Does this furnace have a draft inducer blower? What is the model number of the furnace? One problem in Florida, there are not many that know gas furnace's. AC techs everywhere and most only know electric heat elements in air handlers.
 

gcc

Member
Messages
33
Reaction score
0
Points
6
Location
Tampa, FL
Surprised you have a gas furnace in Florida since our heating needs are short except this week. I know nothing about this furnace, however it sounds the there is not enough air supply and things seems to work when the door is removed that allows more air. One clue is you mentioned "exhaust vents" get very hot. Another possibility is there is not enough air flowing over the plenum to absorb the heat and allowing the exhaust temps to get too high.

From a google search.
Furnaces have a safety component that will detect when a flame rollout occurs — the flame rollout switch. This switch stops the supply of gas to the furnace if the temperature outside the combustion chamber exceeds a certain level.

So what is this 4" vent. Is it the chimney? 3" would never be used for a furnace exhaust vent. It could be a fresh air supply. It appears there isn't enough draft and the plenum is getting too hot. Does this furnace have a draft inducer blower? What is the model number of the furnace? One problem in Florida, there are not many that know gas furnace's. AC techs everywhere and most only know electric heat elements in air handlers.
Here is a pic of the vent I am talking about. It comes out of the furnace and goes up into the attic. In the ceiling /attic is a box that connects the pipe you see into a smaller 3” pipe of the same type of material as you see there, it’s just small. That goes straight up through the roof. I’m wondering if the 3” is a bottleneck for it. But like I said, when I took the furnace door off it didn’t shut down.

I got on the roof tonight and checked but I didn’t see any obstructions info he roof vent hood or whatever it is called.. Steam was coming out of the vent.

I should say - the house was built in 2003. We replaced the original a/c - gas furnace unit in 2013 to this one. It is model 313AAV060110ACJA. It does have a draft motor and I see it spinning when it is on. We use the heat so infrequently that I really don’t know if this has been happening previously, but what caught my attention was the fact that the thermostat would be dead - no power - when it got cold in November. I thought it was an electric issue until I realized the whole system was being shut down by the furnace through that code.

Thanks.
Greg

12A65E63-A902-48E2-922C-7629530E46BD.jpeg


10121247-2D4D-4C4F-A6D3-D86D598970EF.jpeg


12A65E63-A902-48E2-922C-7629530E46BD.jpeg
 

John Gayewski

In the Trades
Messages
1,919
Reaction score
487
Points
83
Location
Iowa
It looks like you have that in a tiny room. Since there is no fresh air intake as a high effeciancy would have you need plenty of makeup air provided by the room in which the unit sits. I'm guessing/ hoping the door of that utility closet as a louvered door?

Also that flex connector is not proper. Should be a hard metal duct. Generally not aluminum. Your combustion gas is hotter than a high effeciancy unit that is generally piped with pvc.
 

WorthFlorida

The wife is still training me.
Messages
4,645
Reaction score
699
Points
113
Location
Orlando, Florida
Yes john, very common on the Florida when an air handler is inside the home and not in the garage. There are no basements for most of the south. You should see the closets in condo's and apartments, even smaller.

GCC, This is getting beyond my skill set but it all seems to point one of two things. That flex pipe is the exhaust (flue) for the burned gases. It could be possible that there is not enough draft and the temps are getting too high or too much back pressure.
Another possibility is on air handler systems, the blower runs at a slower speed in heat mode than the plenum is not getting enough air flow and the temperatures rise.

As asked by John, is the closet door louvered? When the system fails is the closet door still opened and the air handler cabinet door is on?

BTW... when the system shuts down on an error, it removes the 24vac. Thermostat and other components (relays that turn on gas valves and blowers) run on 24vac, therefore, the thermostat has no power and the screen goes blank. Thermostats that have batteries, the thermostat screen will still be active but it will have control because of no 24v's.

Good info on code 33. It all points to air restriction.

What is a draft inducer?

A draft inducer is a fan that’s located inside of your furnace near the heat exchanger. When your furnace begins a heating cycle, the draft inducer is one of the first devices that turns on. In fact, the draft inducer starts up 30-60 seconds before the burners are lit and continues to run throughout each heating cycle.
By turning on before your furnace ignites its burners, the draft inducer is able to clear out any combustion gases that might be lingering in the heat exchanger from the previous heating cycle. Those gases are pushed into your system’s flue pipes and vented out of your home. After the burners do ignite, the draft inducer continues to run in order to provide the burners with a constant source of oxygen.


See page 2.
See page 25.
 

WorthFlorida

The wife is still training me.
Messages
4,645
Reaction score
699
Points
113
Location
Orlando, Florida
Check the size of the opening where the cold air return is and the return grill size. I've seen where the cutout of the wood box air handlers sits on are just not large enough. Have you tried it without any filter? Your furnace uses an ECM motor for the blower, just about common everywhere but it usually limits any control over the blower speed adjustments as in days past. Look on the control board if there are any switches for blower speed?
 

gcc

Member
Messages
33
Reaction score
0
Points
6
Location
Tampa, FL
It looks like you have that in a tiny room. Since there is no fresh air intake as a high effeciancy would have you need plenty of makeup air provided by the room in which the unit sits. I'm guessing/ hoping the door of that utility closet as a louvered door?

Also that flex connector is not proper. Should be a hard metal duct. Generally not aluminum. Your combustion gas is hotter than a high effeciancy unit that is generally piped with pvc.
The furnace/air handler sits on the plenum and the air gets sucked in through the bottom. That part has a door on it and seals it, so whether it was in that closet or not it would get the same amount of air. I took the door off the furnace and it worked because it
Check the size of the opening where the cold air return is and the return grill size. I've seen where the cutout of the wood box air handlers sits on are just not large enough. Have you tried it without any filter? Your furnace uses an ECM motor for the blower, just about common everywhere but it usually limits any control over the blower speed adjustments as in days past. Look on the control board if there are any switches for blower speed?
Thanks all. A tech is coming out to look but I was trying to avoid paying again for this. Note - I made a mistake. The vent in the attic is not a 3" flex pipe - I was looking at the wrong one. It is a full on metal vent up through the roof. My bad.

The door is not louvered. It is a full on regular inside door.
 

John Gayewski

In the Trades
Messages
1,919
Reaction score
487
Points
83
Location
Iowa
The furnace/air handler sits on the plenum and the air gets sucked in through the bottom. That part has a door on it and seals it, so whether it was in that closet or not it would get the same amount of air. I took the door off the furnace and it worked because it

Thanks all. A tech is coming out to look but I was trying to avoid paying again for this. Note - I made a mistake. The vent in the attic is not a 3" flex pipe - I was looking at the wrong one. It is a full on metal vent up through the roof. My bad.

The door is not louvered. It is a full on regular inside door.
Guarantee that furnace CANNOT be in a room of that size without either a makeup duct usually 8". Or the door needs to be louvered. Usually it actually both there should be a fresh air supply and the door is louvered in a room that size. The plenum you speak of likley has nothing to do with combustion air. Combustion air and makeup air from the house are two different things in different chambers with different air supplies.
 

Fitter30

Well-Known Member
Messages
2,527
Reaction score
386
Points
83
Location
Peace valley missouri
Could have a bad limit or roll out switch. With power off pull on wires going to the limit not real hard see if there tight. Roll out switch its in front of the burners look at the flame before blower comes on and when running. See if the flame with blower on flame changes from off. Changes possible bad heat exchanger. Plastic handle screwdriver tap on controls with the handle. Take a pic of wiring diagram on blower door.
 

gcc

Member
Messages
33
Reaction score
0
Points
6
Location
Tampa, FL
Guarantee that furnace CANNOT be in a room of that size without either a makeup duct usually 8". Or the door needs to be louvered. Usually it actually both there should be a fresh air supply and the door is louvered in a room that size. The plenum you speak of likley has nothing to do with combustion air. Combustion air and makeup air from the house are two different things in different chambers with different air supplies.
Oh wow. How does the combustion air get in it? It looks as though the only air making it into the unit is coming from the plenum. Not sure how else air would get in. There is a door in front of the furnace that is screwed on. When you take it off you can access the control board and blower motor, but also the big plenum. The entire bottom is open to it.

The tech thinks that the issue is not enough return vents. Says that the heat can’t get out fast enough through the return vents we have.

Not sure how much adding vents or making the ducts / outlets bigger will cost. There doesn’t seem to be anything wrong with the furnace itself.
 

John Gayewski

In the Trades
Messages
1,919
Reaction score
487
Points
83
Location
Iowa
Oh wow. How does the combustion air get in it? It looks as though the only air making it into the unit is coming from the plenum. Not sure how else air would get in. There is a door in front of the furnace that is screwed on. When you take it off you can access the control board and blower motor, but also the big plenum. The entire bottom is open to it.

The tech thinks that the issue is not enough return vents. Says that the heat can’t get out fast enough through the return vents we have.

Not sure how much adding vents or making the ducts / outlets bigger will cost. There doesn’t seem to be anything wrong with the furnace itself.
Do you see the front of the furnace in the picture you posted? See how the front is louvered? That's your combustion air intake. It relies on the room air to make combustion. The room needs so many cubic feet of air per btu. Something like 10 cu.ft of air, per 1000 btu. If that's not possible you need fresh air makeup and a louvered door.
 

gcc

Member
Messages
33
Reaction score
0
Points
6
Location
Tampa, FL
Do you see the front of the furnace in the picture you posted? See how the front is louvered? That's your combustion air intake. It relies on the room air to make combustion. The room needs so many cubic feet of air per btu. Something like 10 cu.ft of air, per 1000 btu. If that's not possible you need fresh air makeup and a louvered door.
That makes sense. But when you leave that closet door open it still shuts off. It’s only
When you take that Louvered door off and then unscew the door behind it that covers the bottom (to access the control board) that it stays on. if I were to take that closet door off completely or leave it wide open, it still shuts off.

So does adding another return or supply vent help? I can replace that closet door with an louvered door, but I dont think That would be enough.

Thanks - I totally appreciate the info!
 

John Gayewski

In the Trades
Messages
1,919
Reaction score
487
Points
83
Location
Iowa
That makes sense. But when you leave that closet door open it still shuts off. It’s only
When you take that Louvered door off and then unscew the door behind it that covers the bottom (to access the control board) that it stays on. if I were to take that closet door off completely or leave it wide open, it still shuts off.

So does adding another return or supply vent help? I can replace that closet door with an louvered door, but I dont think That would be enough.

Thanks - I totally appreciate the info!
I think I would change the rollout switches. They are very cheap and could fix the immediate issue although I'm not 100 percent sure about that. After you find the immediate issue then I'd worry about combustion air. But while doing your tests you should have both improper and proper makeup air to test what's tripping.

Try making a cover out of cardboard. Covering the combustion chamber and leaving the return air plenum open. If it stays on you know you need more return air. If it cuts off you know (or are at least pretty sure) it's the combustion side.
 

gcc

Member
Messages
33
Reaction score
0
Points
6
Location
Tampa, FL
I think I would change the rollout switches. They are very cheap and could fix the immediate issue although I'm not 100 percent sure about that. After you find the immediate issue then I'd worry about combustion air. But while doing your tests you should have both improper and proper makeup air to test what's tripping.

Try making a cover out of cardboard. Covering the combustion chamber and leaving the return air plenum open. If it stays on you know you need more return air. If it cuts off you know (or are at least pretty sure) it's the combustion side.
I tested the switches. The limit switch opens when the unit shuts off. I believe that it is working as designed. Tech thinks the unit is just oversized for the ducts we have. That’s a strong possibility. This is rhe 2nd unit we’ve had. The original was a 3.5 I believe. But we changed it out 9 years ago. Not sure why we are just having the issue now. Then again, it’s rarely cold down here so who knows.

Help me understand a concept. The furnace sits on a hole that where all the air comes into the unit through the air intake ducts. (Not sure if they are called return or supply ducts but they bring air into the unit through the filtered vents that suck air in). If you take off the bottom metal door in the pic, you’d see the control board and blower motor and a big hole where the air gets sucked into the unit. I drew on the picture with the cover on so you can follow the airflow into the unit.

When that inside metal door is off and that hole is wide open; the thing works fine and stays on. Could I not just remove that metal door and tape the cut off switch and put the outdoor door on it? What is the purpose of that inner metal door? It has a gasket for an airtight seal.

The tech feels like we need to add some returns and get bigger ductwork. Why can’t i just cut a hole in that inner metal door to let more air in? Or get another door or sheet metal with a hole in it for winter. im not sure how that works or why leaving that door open compensated for not having enough returns or big enough ducts. Just trying to learn.

Thanks,
Greg
 

Attachments

  • 0E8E5D98-B1AD-4286-9870-0A3555C35287.jpeg
    0E8E5D98-B1AD-4286-9870-0A3555C35287.jpeg
    93.6 KB · Views: 29
  • 30476E3C-9EB3-42E4-BC94-CE61C1059FA1.jpeg
    30476E3C-9EB3-42E4-BC94-CE61C1059FA1.jpeg
    93.6 KB · Views: 31
  • 8CD03EB8-0E21-4FBA-A5F8-534C7CDF98B8.jpeg
    8CD03EB8-0E21-4FBA-A5F8-534C7CDF98B8.jpeg
    86.1 KB · Views: 43

Fitter30

Well-Known Member
Messages
2,527
Reaction score
386
Points
83
Location
Peace valley missouri
Corrugated flue pipe is a disaster waiting to happen. Show me the UL label on it. It comes apart hope you have a CO detector.
 

John Gayewski

In the Trades
Messages
1,919
Reaction score
487
Points
83
Location
Iowa
Those two chambers need to be separated. One has carbon monoxide being created. The other is a vacuum or positive pressure depending which side of the fan your on. Carbon monoxide will be distributed throughout your home if those two chambers are exposed to one another.

You should be able to just cut some registers into your return duct. Get a good sized register that is adjustable. That way you can cut a big hole in thr return duct and close the register until it stops working. When it stops working you've gone too far.
 

John Gayewski

In the Trades
Messages
1,919
Reaction score
487
Points
83
Location
Iowa
Also I agree. That flex connector needs to go. I'm about certain it's not legal and it's dangerous. You need a decent gauge thickness of steel duct that is screwed at the joints.
 

gcc

Member
Messages
33
Reaction score
0
Points
6
Location
Tampa, FL
Also I agree. That flex connector needs to go. I'm about certain it's not legal and it's dangerous. You need a decent gauge thickness of steel duct that is screwed at the joints.
That’s disappointing to hear as we paid a professional company to install and it was inspected. Ugh!

That flex pipe is pretty rigid but still flexible. It connects to a steel duct just out of the range of that last pic I sent:
 

Attachments

  • 980E88D1-4715-4EBC-AED9-854343630F37.jpeg
    980E88D1-4715-4EBC-AED9-854343630F37.jpeg
    62.5 KB · Views: 28
  • C7936F54-04C9-47F9-B163-536C62112AF9.jpeg
    C7936F54-04C9-47F9-B163-536C62112AF9.jpeg
    65.4 KB · Views: 29

Fitter30

Well-Known Member
Messages
2,527
Reaction score
386
Points
83
Location
Peace valley missouri
80° rise is the max air supply from the return temp. 70° return 150° supply. Counter flow furnace also has a limit in the blower compartment might be attached to blower housing. If blower motor is plug into the red wire change it to blue which is medium speed.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks