I have a Goodman GDS80904BNA downflow furnace that does not work. It is 3 years old. I am getting the open limit switch error code on the circuit board when the T-stat call for heat. Only the circ. blower turns on and rans continuously until I turn it off.

Here is a little history on it. Once Every couple weeks this winter the furnace would act up. It would try to fire 3 times but it would not and shut down. A few minutes later it would start with no problem. Or it would start up and run fine for a few minutes but it would not reach the temperature. By the time I would call a HVAC tech it would be working and they told me there is nothing they could until they see it act up. This went on for 4 months. Finally last week it did this continuously for 1 day. By the time the HVAC tech got here the next day it would not even fire up. He replaced the gas valve and it worked good for about 2 days then it would turn off before it reached T-tsat temperature. It seemed to only do this at night. He came back and it worked fine, so he switched T-stats as a test, next night same problem. Now last night only the fan blower will run when heat is called for as stated above. I am waiting for repairman to come back.

Here is a few things I tested. I jumpered the primary limit, pressure switch, and rollout limit each one a time and I get the same open limit error code. I opened all dampers and registers on the supply side. Flame sensor has been replaced also. I don't think the Flue is blocked, but how would I check? Any ideas?

Thanks

The unit is likely equipped with an auxiliary limit inside the blower compartment - a little tricky to get to on this unit. You should (if you didn't already) locate at least 3 roll-out switches surrounding the burner assembly. Follow the purple wires from one to the next, checking for any that are tripped or broken.

There is only one roll out switch installed on the middle, there are knockouts for to add 2 more, 1 on each side. I tried to jumper this with no luck. There is a blue tab on it sticking up about 1/4". I tried to push it down but it won't go down so I assume this is normal operation. I also check the primary limit and rollout switch for power with the volt meter and it reads 0 when the furnace tries to kick on and the circ. blower starts. I will check the Aux. Limit next and see if this works???? What would block the primary limit switch and rollout switch from receiving power. Is there a certain order to be checking these??

Thanks for the response

Ok luckily I had a humidifier installed, I opened up the humidifier cover pulled the humidifier filter and air filter, found the Aux. Limit switch, pulled the 2 wires and reinstalled and tapped on the switch. The furnace fired right up, which is the best progress I had in 2 days. BUT it ran for any a few minutes and turned off. Was at 62 and it went to about 65 when it turned off. tstat was set on 70. Is this a bad aUX LIMIT SWITCH?

Is the auxiliary limit you found a manual-reset type, or auto-reset type? If it is manual-reset, not tripped (you will feel a "click" when you push the center button if it is), and it is losing continuity/breaking the circuit, it is indeed a bad limit.

try bypassing aux limit(only temporarily for testing purposes) If furnace runs long enough to get up to t-stat setting, then replace aux limit. You may also have an air flow problem causing limit to trip. Check filters, and if your furnace is a 90+, you may want to pull blower assembly and check to make sure condensing coil in heat exchanger isnt plugged.(not likely on a three year old furnace, unless you have a few pets, and filter has been neglected for three years). Also, evap coil on ac may be plugged if you have central air. The good news is that the furnace is failing regularly, so the tech that comes to work on it should be able to locate problem(hopefully). Good luck and please let us know what is found.

The Aux Limit is auto reset, it's a 80% furnace and I do have A/C and a dog, I did bypass it Aux Limit switch which I though was bad., still same problem. I bypassed all 3 limit switches (Main, Rollout and Aux) all at one time and still get 4 flashes which is open limit switch. Sometimes it runs good for only a few minutes and sometimes it goes straight to the circ. blower and blows cold air. Is there any more limit switchs that I am not aware of? HVAC tech should be here tomorrow, he couldnt get here on a sunday.

Thanks for all the info

look on your wiring diagram located on inside cover of furnace. look to see how many limit switches/ rollouts are on the diagram. At this point, if all limits/ rollouts have been jumped, therefore eliminating them as the problem, yet led diagnostic light still shows open limit, i would say you have a bad board. I have had this exact thing happen on a two year old goodman , only it was an upflow. the four flash was confusing, because all limits checked out just fine. Im betting on the board at this time. please let us know what the tech finds. When a diagnostic code does not read a correct fault, usually it is the board. But it is still best to have out the tech and have him trouble shoot furnace as he normally would.

Thats what it was, A bad circuit board, he switched it out and so far so good. The back of the old board was discolored where most of the transistors were. I did notice that the new circuit board was different. Some of the transistors were larger than the original. Just a guess but maybe the transisitors were too small and they fixed the problem on the replacement circuit board.

Thanks again for all your help.

just glad it got fixed. Take care.