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RUUD furnace sparking not lighting

Working on RUUD furnace sparking but gas valve not opening tested voltage at gas valve the reading jumps all over the place and reads negative re placed control board and same  thing is still happening can anyone tell me what is going on
 model RGRC-10EZAJS
serial HM5D707F411104896


    EBEBRATT-Ed Member Posts: 15,346
    edited January 2021
    Are you getting voltage at the transformer of 24 volts ok? Sounds like a loose wire, a safety not making contact or something shorted. Check all the wiring connections and follow the circuit through. Use an ohmmeter to check continunity through everything.

    If you have a spare transformer power the gas valve with 24 volts with the GAS SHUT OFF to see if the valve works and the voltage is steady. Then follow the circuit back to see where your losing it. Is one side of your transformer grounded? Polarity correct?
  • HomerJSmith
    HomerJSmith Member Posts: 2,408
    edited January 2021
    Are you sure the gas shut off valve is open and that gas is present? Check incoming gas pressure. It should be 7" Water/Column to the gas valve.

    Loosen the flex connector connected to the pipe that goes to the gas valve or if it is solid pipe loosen the ground coupling or remove the small plug in the input on the gas valve and see if gas is present and check the pressure there.
  • Jamie Hall
    Jamie Hall Member Posts: 22,949
    And check all your possible ground connections -- right back from the boiler to the switchgear.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • HomerJSmith
    HomerJSmith Member Posts: 2,408
    edited January 2021
    I guess the gas valve knob is in the on position and the polarity of the receptical and the connection to the IFC are correct. Are there any LED blink codes?

    Check gas supply and manifold pressure.- Ensure L1 and Neutral not swapped on IFC and receptical or junction box.- Check SE alignment.- Check orifice or other restrictions to gas flow.- Check flame sense rod (clean with sandpaper).- Check flame carry over.

    Check wires, continuity, and connection between IFC and gas valve. Ensure 24 V between appropriate pins on connector of IFC. Ensure manual switch on valve is in the “ON” position. 90+ check aux. limit open? Should be closed. 90+ upflow models check drain pressure switch between IFC and gas valve. should be closed – replace drain pressure switch if drain is not blocked or clear drain if blocked.- Did a pressure switch open during ignition trial? Did a limit open during ignition trial? Go to figure 56, see the link.

  • steamhammer
    steamhammer Member Posts: 4
    it was bad drain pressure switch