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Rheem Short Cycling Troubleshooting

I have a Rheem Criterion RGDJ-12EARJR. I've been having an issue with it short cycling. The burners will ignite and shut off a few seconds later.

I have cleaned the Flame Sensor and I have replaced the Flame Sensor neither of which fixed the issue. Following the Troubleshooting guide that Rheem provides I then checked the Ground and Polarity of the IFC board and those were good. I replaced the IFC board as last measure of the Troubleshooting guide and that has not fixed the issue. For sanity I replaced the Flame Sensor a second time to ensure it was not that.

All the symptoms point to the flame sensor or IFC board however the issue was not corrected after replacement of either. I cannot see any DC current on the Flame Sensor to the IFC board (I see AC of about 4 uA). I have continuity on the wire from the flame sensor to the IFC board.

The flame looks nice and blue for the few seconds it is on.

Any other checks I should do to isolate the issue? If it is the Gas Relay Valve I don't intend to try and fix that myself.

Comments

  • IronmanIronman Posts: 5,211Member
    Have you checked the ground wire ALL of the way back to the service panel? You MUST have good ground continuity all the way to the service disconnect for the furnace to prove ignition.

    Tip: TEMPORARILY grounding the furnace neutral to the furnace cabinet will tell if the ground path is good. If it stays lit with the neutral grounded at the furnace, then the ground path is faulty.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • Yes, I have checked the continuity of the ground wire to the panel. It is a dead short from the lead to the posts in the box, as it should be.
  • I should also mention I wanted to make sure the vent wasn't clogged, so I took the vent pipe off of the inducer fan housing for a test. The device still would not stay on and exhibited the exact same behavior of igniting then turning off. I also took the inducer fan off to check to see if the inducer was clogged and I see no evidence of that.

    I figured I might as well be thorough.
  • IronmanIronman Posts: 5,211Member
    Have you checked the condensate drain including the outlet at the collector box? A clogged, or partially clogged drain can exhibit the symptoms you describe. So can water in the pressure switch. Check the drain and if that's ok, place your volt meter leads across the pressure switch terminals. If it shows voltage when the furnace fires, then the switch is opening. Then find the cause.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • This particular model doesn't have the condensate drains. Not high efficiency. The pressure switch is definitely dry. I took the hose off the pressure switch to check that as well.
  • JUGHNEJUGHNE Posts: 5,986Member
    edited October 2017
    Does this have a separate flame sensor and a separate Hot Surface Igniter or spark?
    How old is this?
  • No older than '95. Separated Hot Surface Igniter and Flame sensor. Igniter on the first flame and the Sensor on the last flame. Two flames between them.
  • JUGHNEJUGHNE Posts: 5,986Member
    Early retrofit was to add FS and connect to existing HSI neutral/white wire only. It is an obvious add on. If your HSI has any leak to ground then it could be eating your FS signal.
  • It looks like this wasn't retrofitted but designed this way. I gather that from how the devices are laid out and from the schematic drawings on the service panel.
    However, I'll check the grounding and the neutral lines again when I get home this evening. It's worth a shot.
  • IronmanIronman Posts: 5,211Member
    Check for a hairline crack in the HSI.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • HVACNUTHVACNUT Posts: 2,512Member
    Are you able to check manifold gas pressure?
    I assume it's a single stage furnace.
    Natural gas? Should be 3.5" WC manifold.
    Do all the burners fire up right away, or does is take a second to ignite the burner with the FS?
    Shut down. Remove the burners. 1/4" hex head screws on top hold them together. Brush them out. Take a paperclip and make sure all 4 orifices are clear.
  • I don't have any way to check the gas pressure. If it comes to that I'll let an experienced professional work on that.
    For the most part the flames ignite at the same time. Minor delay but nothing significant.

    So I went back and checked the grounding again. No issues present. The HSI has a designated path and doesn't share its neutral line. The FS goes straight into its molex and then into the board.

    While I was working on it, I let the system attempt to ignite but it wouldn't. So I turned off the heat and left on the fan and that's when it finally threw a new error code besides "system lockout". The system said the pressure limit switch was open.

    After looking at the diagram I realize that this might explain the lack of rectified current to the IFC board from the FS. I think my pressure switch is operating at the edge of failure. It's operational enough to allow ignition but it's not actually closed enough to allow the micro-amps through for flame detection.

    I'll pick up the part in the morning and then attempt to fix it. I'll let you all know. Appreciate your help.

    If you can think of anything else that it might be in the meantime I'll look into it.
  • JUGHNEJUGHNE Posts: 5,986Member
    edited October 2017
    Sequence of operation might be something like this:
    Tstat starts inducer fan, runs for certain pre-purge time.
    Pressure switch activates igniter module
    HSI starts to glow, red hot for certain time frame
    HSI off and pilot light gas on, lighting from residual glow of HSI.
    FS confirms fire and allows main gas valve to open.
    (Now main fire on could......blow flame away from FS causing shutdown..............or cause enough change in pressure to affect borderline pressure switch to shutdown.)

    You have come this far and may as well change the HSI before the pressure switch.
    I don't know if Rheem uses this as a second FS as they did when the retro kits came out. HSI does not make a very reliable FS.

    Note: if your gas valve has a switch/knob to shut off the main gas valve you might be able to leave the pilot burn just to see if it holds on.
    This works for commercial gas set ups anyway.
    Picture of gas valve might help.
  • John Mills_5John Mills_5 Posts: 923Member
    With DC microamp meter in series with flame rod, when firing should be up over 3 DC micro amps with a clean rod.
  • unclejohnunclejohn Posts: 1,420Member
    Just jumper the pressure switch after the inducer fan starts and see it the burners stay lit. If so replace switch .
  • BenRestinBenRestin Posts: 3Member
    99 % of the time, cleaning the flame sensor solves the problem, if that spade clip is not tight, or the spade has rusted. But you replaced it, was it the same shape...and is it in a blue part of the flame? Your pressure switch is good enough to prove the vent and run for seconds to operate the hot surface and light. I think it is still in the FS function, look at the moldex connector and make sure the Orange wire is seated and not pushed out one side, it might show continuity
    with a touch but not good enough to function.
    Funny thing about pressure switches, dealers wanted them replaced exactly to match the suction or pressure, now dealers are stocking general range replacements. Go figure???
    Another thing, do you still have your old board?
    Another state of affairs you could have a bad board, this is where a service tech can save you some money, cause when you buy aboard it is warranted about that long, buy another board.
    I carried a second board just in case and this is a rough deal but l have been able to return a bad board cause it didn't work, and boy those trouble shooting ladders are really free with replace ICB..

    Ben Restin
  • MikeMike Posts: 94Member
    While your at it, check voltage and amps of inducer motor. It may not be coming up to full speed. Rpms are the only real way to do this. But a amperage reading could give you hint. Low Rpms can cause the pressure switch not to make
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