Biggest reason I have found is increased gas pressure effecting the delta t across the heat exchanger......readjust the manifold gas pressure and the problem goes away. It's not just the air side that needs checked. This is the major cause of exchanger failures. Fit the furnace to the duct system, as opposed to the the idea that the ductwork was designed for the furnace that was installed.
I just wanted to post on here and mention what I did. Previous to seeing this video, I did every bit of trouble shooting. I have one vent that is partially blocked, but cant do anything about. I added another cold air return in my return in the basement, and cut a vvent to heat the basement as well. Was still kicking. The only thing that seems to work is to put high speed setting on the blower.
High, question for you, I have a Gibson KG7SD 038D-23EB, IT KEEPS TRIPING OUT ON HIGH LIMIT, It will startup fine, going through sequences... runs about 6-8 minutes then burner quits, ventor motor stays running for about 1.5-2 minutes more then stops as well, BUT the blower stays running, only way to shut it down is, turn thermostat down so it quit calling for heat, then it does stop. If i turn it back up, it calls for heat but the BLOWER & VENTOR motor starts running, the ventor runs about 1.5-2 minutes then shuts down, fan stays running??? I can get the furnace to start again by resetting the High Limit, but then it does the whole sequence all over again any suggestions? No, to plugged filter, even removed it leaving door open so no supply air problem. No to blocked vents, even took a 8" plenum off just to allow better heat flow out? No to blocked exhaust vent its comes out through furnace to the "T", 2" pipe goes up 50" then 90 elbow, over about 36" to Concentric vent out through the wall on the board, I've increased "FAN" to highest level, "H" where it has the heat and cool settings i moved the heat down 1 increment at a time to lowest heat setting... still same issue??? any thoughts on what to try - how to fix...
Carrier furnace: started cutting off and on 3 times or so when thermostat reached temp. Finally thermostat went blank. Changed out thermostat, Replaced the circuit board, good voltage on both sides the xformer, good continuity on the high limit switch. What am I missing?
Money unit has two thermal switches on the high side feeding the electric coil. Both are tripping and taking about 10 minutes to reset as they cool down. They both show around zero ohms normally closed and when they trip they're definitely open. The entire indoor shuts down when this happens. I've got plenty of air flow all the panels off plenty of air coming out the vents and the property heats up but right at 61° on the thermostat the indoor kicks off every time. The blower motor is running the whole time until the thermal overload. Since both thermal switches are acting the same and the blower motor is blowing lots of air and there's plenty of air flow I'm stuck on what this might be?? Is it possible for an electric heater coil to be too hot? Is that a failure mode they exhibit?
Usually if it's tripping there's a reason. Most of the time the switch is doing what it's designed to. Check airflow. Filter, secondary, evaporator, supply, return.
Great video, thanks. I have a question. Our limit switch tripped due to overheating but would not reset and with the help of a local technician I tested the resistance and found that the switch was faulty. I replaced the switch and had to reset a blower/auxiliary switch as well and got it all up and going. However, the upper blower limit switch would still trip every few weeks, mostly in the morning when the heat was coming on to warm a cold house. We could go months without tripping it. So I bought a new switch and it seemed to help but now it’s tripping every other day in the morning. What could be the cause? My filter is clean. The lower blower limit switch doesn’t trip, just the upper one (hotter I assume). Could my fan be underperforming? I have had to replace my fan capacitor a couple times. Maybe it’s due again? It’s a York Diamond 80 furnace.
There is one more scenario, my American standard high efficiency furnace has an unadjustable 45 seconds heat exchanger warm up timer before blower kick in, this is really stupid design. Sometime this 45 seconds warm up period will trip the high limit switch if this heating circle start too soon before heat exchanger didn't cool down enough from previous heating circle. It should use a fan start switch like old system to control the blower instead the fixed timer.
A short cycling furnace's common causes include a malfunctioning thermostat, clogged air filter, clogged flue, dirty flame sensor, damaged igniter, fan limiter failure, and oversized furnace. Be sure it has good airflow in and out of the unit.
I have a York diamond 80 and it keeps overheating which causes it to cut off but it's weird because it will cut off for a few minutes then cut back on and it just continues to do this and will not lock out. I noticed that inside the furnace it seems like their is hot air blowing back in from one of the vents like there's something that's restricting the sure from going out.
@@veevee1209 normally it means your furnace is overheating.. whether that be obstruction thru the ducts or a dirty filter..I tend to do what's the cheapest first and a filter is like 3,4 bucks.
Biggest reason I have found is increased gas pressure effecting the delta t across the heat exchanger......readjust the manifold gas pressure and the problem goes away. It's not just the air side that needs checked. This is the major cause of exchanger failures. Fit the furnace to the duct system, as opposed to the the idea that the ductwork was designed for the furnace that was installed.
Several good places to check. Thanks.
I just wanted to post on here and mention what I did. Previous to seeing this video, I did every bit of trouble shooting. I have one vent that is partially blocked, but cant do anything about. I added another cold air return in my return in the basement, and cut a vvent to heat the basement as well. Was still kicking. The only thing that seems to work is to put high speed setting on the blower.
Great information and great presentation. Thanks!
High, question for you, I have a Gibson KG7SD 038D-23EB, IT KEEPS TRIPING OUT ON HIGH LIMIT, It will startup fine, going through sequences... runs about 6-8 minutes then burner quits, ventor motor stays running for about 1.5-2 minutes more then stops as well, BUT the blower stays running, only way to shut it down is, turn thermostat down so it quit calling for heat, then it does stop.
If i turn it back up, it calls for heat but the BLOWER & VENTOR motor starts running, the ventor runs about 1.5-2 minutes then shuts down, fan stays running???
I can get the furnace to start again by resetting the High Limit, but then it does the whole sequence all over again
any suggestions?
No, to plugged filter, even removed it leaving door open so no supply air problem.
No to blocked vents, even took a 8" plenum off just to allow better heat flow out?
No to blocked exhaust vent its comes out through furnace to the "T", 2" pipe goes up 50" then 90 elbow, over about 36" to Concentric vent out through the wall
on the board, I've increased "FAN" to highest level, "H" where it has the heat and cool settings i moved the heat down 1 increment at a time to lowest heat setting... still same issue???
any thoughts on what to try - how to fix...
Carrier furnace: started cutting off and on 3 times or so when thermostat reached temp. Finally thermostat went blank. Changed out thermostat, Replaced the circuit board, good voltage on both sides the xformer, good continuity on the high limit switch. What am I missing?
What about gas pressures can that be a reason as well? If they were never adjust properly upon install?
Yes
Definitely
Yes, I've seen some set over 4.25 wc bc they just slap them in and get out asap. Check temp rise, blower speed.
This must be my situation. My gas meter was replaced just after the cold season.
Money unit has two thermal switches on the high side feeding the electric coil. Both are tripping and taking about 10 minutes to reset as they cool down. They both show around zero ohms normally closed and when they trip they're definitely open. The entire indoor shuts down when this happens. I've got plenty of air flow all the panels off plenty of air coming out the vents and the property heats up but right at 61° on the thermostat the indoor kicks off every time. The blower motor is running the whole time until the thermal overload. Since both thermal switches are acting the same and the blower motor is blowing lots of air and there's plenty of air flow I'm stuck on what this might be?? Is it possible for an electric heater coil to be too hot? Is that a failure mode they exhibit?
It would have been helpful if you had explained how to check the limit switch. How is that done?
Continuity my friend
Usually if it's tripping there's a reason. Most of the time the switch is doing what it's designed to. Check airflow. Filter, secondary, evaporator, supply, return.
Great video, thanks.
I have a question. Our limit switch tripped due to overheating but would not reset and with the help of a local technician I tested the resistance and found that the switch was faulty. I replaced the switch and had to reset a blower/auxiliary switch as well and got it all up and going. However, the upper blower limit switch would still trip every few weeks, mostly in the morning when the heat was coming on to warm a cold house. We could go months without tripping it. So I bought a new switch and it seemed to help but now it’s tripping every other day in the morning.
What could be the cause? My filter is clean. The lower blower limit switch doesn’t trip, just the upper one (hotter I assume). Could my fan be underperforming? I have had to replace my fan capacitor a couple times. Maybe it’s due again? It’s a York Diamond 80 furnace.
Don't be a cheapskate. Call a pro when all else fails. You're being very cheap for someone who has a good amount of money
There is one more scenario, my American standard high efficiency furnace has an unadjustable 45 seconds heat exchanger warm up timer before blower kick in, this is really stupid design. Sometime this 45 seconds warm up period will trip the high limit switch if this heating circle start too soon before heat exchanger didn't cool down enough from previous heating circle.
It should use a fan start switch like old system to control the blower instead the fixed timer.
I have a goodman with a issue 4 flashes = open high limit ,replaced the high limit sensor work for a min them the same situation the 4 flashes
Did u ever find the cause
Mine keeps short cycling even with a new switch. 2 plumbing companies and numerous new parts has mot fixed it yet. Dont know where to turn next.
A short cycling furnace's common causes include a malfunctioning thermostat, clogged air filter, clogged flue, dirty flame sensor, damaged igniter, fan limiter failure, and oversized furnace. Be sure it has good airflow in and out of the unit.
Airflow
I have a York diamond 80 and it keeps overheating which causes it to cut off but it's weird because it will cut off for a few minutes then cut back on and it just continues to do this and will not lock out. I noticed that inside the furnace it seems like their is hot air blowing back in from one of the vents like there's something that's restricting the sure from going out.
Update?
@@ag86fox Lol I still haven't figured it out..
@@pimp1979robertmack damn lol
Weird. I have the same furnace and having issues. Not the same ones but my limit switch was faulty and then now the blower switch keeps tripping.
@@veevee1209 normally it means your furnace is overheating.. whether that be obstruction thru the ducts or a dirty filter..I tend to do what's the cheapest first and a filter is like 3,4 bucks.