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Rheem Super Quiet 80 Series Limit Switch Tripping

JGAM
JGAM Member Posts: 7
Rheem Super Quiet 80 gas furnace only works when the Burner Compartment door is removed. Its inside a closet, and even if the Burner Compartment Door is removed (but the closet door is closed) one of the Limit Switches will trip and shut down the burners, leaving the blower running.
I have replaced both Limit Switches, made sure the filter is clean. Please advise.

Comments

  • unclejohn
    unclejohn Member Posts: 1,757
    Return air grills blocked? Is it a standard filter or a very hi eff. one. Don't use filters over a 8 rating, too restrictive. If it runs with the door off you have a air flow issue some where.
  • JGAM
    JGAM Member Posts: 7
    I am getting three LED blinks with a two second pause when it happens. I found this online with reference to Rheem Furnaces:-

    Three LED blinks with a two-second pause indicates the limit switch is closed. A limit switch is a safety feature directly wired into the furnace; it stops a furnace from overheating if air isn't properly flowing through the heat exchanger. If the switch is closed, debris might be clogging the filter or the blower fan housing.

    My filter is new and clean. Do I need to dismantle the housing to check if the fan is blocked with debris? I have always changed my filters regularly and doubt if the blower fan is blocked. Please advise.
  • Jamie Hall
    Jamie Hall Member Posts: 18,947
    Not enough air. Maybe not enough combustion air, maybe not enough return air to the heat exchanger, maybe both. Where is the furnace getting its combustion air from? This part of your initial comment: "only works when the Burner Compartment door is removed. Its inside a closet, and even if the Burner Compartment Door is removed (but the closet door is closed) one of the Limit Switches will trip and shut down the burners, leaving the blower running" is concerning.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JUGHNE
    JUGHNE Member Posts: 9,763
    Assuming the 80 implies an +80% furnace, there were some that had outside air piped into the furnace.
    Is yours set up that way? If so does it have a combustion air inlet pipe that is open to somewhere?
  • JGAM
    JGAM Member Posts: 7
    This unit was installed in 2007, no problems until last year. Nothing has changed in the closet that its located inside.
    I was in the attic last week and reconnected one of the ducts to a (cold) bedroom that had completely come apart. Air flow seems good at all registers.
    The second photo shows the only way the furnace works, top panel removed and closet door open.





  • unclejohn
    unclejohn Member Posts: 1,757
    edited February 2018
    Is your closet door solid or louvered? On your furnace there should be a error code specific to your model use that for the blinking light. Are the limits that trip the ones right above the burners that have to be reset? Those are flame roll out switches. Has the room been tighten up so that less cold air leaks out and therefore less combustion air gets in?
  • HomerJSmith
    HomerJSmith Member Posts: 1,563
    edited February 2018
    Do a temperature rise on the furnace and check blower speed.

    If the high limit switch trips, you have insufficient flow across the HX.

  • HomerJSmith
    HomerJSmith Member Posts: 1,563
    Rheem and Rudd filters that came with the furnace is the only filter to use. It is an electrostatic filter that is easily washed in the bath tub. It has a high flow rate. You don't have one in your furnace.
  • HomerJSmith
    HomerJSmith Member Posts: 1,563
    You are not suppose to use Corrugated Stainless Steel Tubing (CSST) thru the cabinet. It should be a blk iron nipple.
  • HomerJSmith
    HomerJSmith Member Posts: 1,563
    If it is a roll out switch that tripping you have a blocked flue or a Induced Draft Motor problem.
  • HomerJSmith
    HomerJSmith Member Posts: 1,563
    Your air conditioning evaporator clean?
  • HomerJSmith
    HomerJSmith Member Posts: 1,563
    Spin the Induced Draft Motor by spinning the black disk by hand.
    It should rotate smoothly without binding. This does't mean that the blower wheel isn't loose on the shaft and not rotating properly.
  • HomerJSmith
    HomerJSmith Member Posts: 1,563
    "Three LED blinks with a two-second pause indicates the limit switch is closed. A limit switch is a safety feature directly wired into the furnace; it stops a furnace from overheating if air isn't properly flowing through the heat exchanger. If the switch is closed, debris might be clogging the filter or the blower fan housing."

    This doesn't make sense to me. High limit switches are normally closed and open on a high temperature event, the same as the roll out switches. The high limit switch can also trip if there is a failure of the HX and exhaust gases are raising the blower temperature across the HX. But we're talking about the two roll out switches with the red reset button on them, right? Not the High Limit that's tripping.

    Look at the flame with the closet door open. It should be fiercely
    pulled in to the HX tubes by the Induced Draft Motor. Close the closet door and observe the flame. Any change?
  • JGAM
    JGAM Member Posts: 7
    The switches that trip are the two directly above the burners, and the right side one in particular (red arrow). There is an inch and a half gap at the bottom of the closet door, no louver.

    I had removed the air filter for the photos.

    A/C Evaporator was blown & hosed clean last summer as it blocked up with sludge.

    The flame is fiercely pulled into the tubes when the cover is both on and off (there is a small window on the cover) and looking through a small crack in the closet door when mostly closed, the flame is still pulled in the same.

    I checked the flue pipe on the roof this morning, and it was cler all the way down to the angle on top of the furnace. Will pull that apart today and check it from below.

    The installation booklet Blink Codes state: 3 Blinks - Limit Circuit Open - CHECK THE FOLLOWING - Airflow. Limits, Rollouts, Overfire.


  • SuperTech
    SuperTech Member Posts: 1,792
    That's definitely the roll out switches. In my experience most of the time they are tripped by flame rollout caused by heat exchanger failure. I would recommend contacting a professional who is experienced with combustion testing.
    Especially considering you replaced the switches and still having issues it's very likely that your heat exchanger has failed and the switches are doing their job.
  • ratio
    ratio Member Posts: 3,178
    Those are roll out switches. The fact that they're tripping indicates a more serious problem than excessive temperature rise—they are to protect against flames coming out of the burner area.

    You should shut it off and call for service. Carbon monoxide poisoning or a fire are two results from excessive flame roll out.

    SuperTech
  • unclejohn
    unclejohn Member Posts: 1,757
    You need to shut it off and call a pro.
  • JUGHNE
    JUGHNE Member Posts: 9,763
    There is a small chance that the exhaust inducer fan is not to full capacity.

    The roll out limits have the manual reset button on them for good reason...........to get you to call for help.

    Some flame roll out limits are a one time fuse, non resettable .......again to get you to call for help.
  • JGAM
    JGAM Member Posts: 7
    Thank-you for the advice. I shall contact an HVAC Pro. for help. I was wondering though, if the heat exchanger is suspect, why there is no sign of flame roll out when the burners are on. The flames are blue and steady and enter the heat exchanger completely, regardless of whether the cover panel is on or off?
  • SuperTech
    SuperTech Member Posts: 1,792
    A normal looking flame should never be considered an indication of safe operation.
    With the precise instruments available to technicians today there's no excuse not to test appliances the correct way.

    Going by sight is really a primitive, caveman mentality.

    Imagine a doctor giving you a clean bill of health without taking blood pressure because you "look healthy".
    CanuckerDan Foley
  • DZoro
    DZoro Member Posts: 1,048
    Those rollouts are sensing high heat that shouldn't be there. Something is amiss, have to properly check all avenues until the source is found. Possible if you don't use or change the filter often that the A- coil might be plugged. Just one of many possible problems.
  • DZoro
    DZoro Member Posts: 1,048
    The main door to your furnace room. It looks like a solid core door, has it always been there? Is there any gap under the door when it is closed? Does anything ever get put on the top of the furnace? Try running it with the furnace doors on and keep the closet door fully open.
  • JGAM
    JGAM Member Posts: 7
    Dennis, the closet door is the same solid core door that has been there since the furnace was installed in 2007. It has 1 1/2" gap at the bottom. Never any problems until recently. I tried running it with the furnace panel on & the closet door open, but the switch trips. The closet door and the panel cover both need to be off for the burners to remain lit.
    As I mentioned before, the filters are changed regularly, the fan blows well and the flue is clear. I also installed two new switches. You mentioned the A-Coil may be plugged? Do you mean the a/c evaporator coil? Could a blockage in this affect the function of the furnace? I had to hose out the a/c drain this past summer and it was full of sludge.
  • ratio
    ratio Member Posts: 3,178
    I wouldn't expect a plugged A-coil (the air conditioning coil, I hope it's not an N-coil!) to directly cause a roll out. A plugged A-coil would cause excessive ΔT that could cause a cracked HX. The blower would then pressurize the HX, causing the flames to roll out.A quick check is to watch the flames during the beginning of a heating cycle. If they dance the Tango when the blower comes on, you've got a crack in the HX.

    NOTE: this is just a quick visual check that will catch the pathological case, a combustion analyzer MUST be used to be sure the burn is clean and safe.

    The last roll out switch trippage that I came across was caused by the plummer putting too much torque on the gas valve, enough to mis-align the burners. <sigh>

  • JGAM
    JGAM Member Posts: 7
    During the beginning of a heating cycle the flames are blue and steady and enter the heat exchanger immediately and completely, I guess I will know for sure when the service tech does a combustion check.
  • DZoro
    DZoro Member Posts: 1,048
    @JGAM The fins on the A-coil are the most restrictive part of your system besides the filter. So yes crud can build up on them especially in the top portion of the A.
    Many H/E's develop cracks in different ways. Yours maybe slowly opening up during a heat run cycle. The metal expands and moves around as it is being heated. Thus sometimes even causing a ping sound and the crack then opens up. You say the flames are nice and steady at the beginning of the cycle, do they change during the cycle especially after a long run cycle?