Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

how to tell if an ignition control module is bad

billtangbilltang Posts: 10Member
edited February 5 in Gas Heating
new Igniter was not getting 110v from the ignition control module (fenwal 2465H 600-003 or 35-655-600-003). When the call to heat comes, the motor runs. There is supposed to be 110v from control module to igniter (which I measured once when it was working) but it is not there. After 45 seconds there is a 24v to gas valve and a click. The valve opens but since there is no flame, it is then 0v and shuts off. During the whole time, the red diagnostic light stays on. According to the spec, this is supposed to be "Internal Control Failure". Does it mean this control module is bad? Thanks!


  • Intplm.Intplm. Posts: 684Member

    Igniter ? New as in installed today ? How long has the igniter been in operation? You might mean to say "Ignition module".
  • billtangbilltang Posts: 10Member
    edited February 6
    The hot surface igniter is a few days old. The resistance is 70ohm. I just replaced one which is of 100ohm. Although that was just a few months old, it is above the 40-90ohm range; according to many online articles, anything above 90ohm is not reliable.

    The ignition control module (fenwal 2465H 600-003 or 35-655-600-003) is about 12 years old.

    The wiring has not been changed. I check common ground to be ok (within 2ohms).
  • Intplm.Intplm. Posts: 684Member
    I hate to say it but it might be toast.
    Was this a direct replacement?
    was there a different ignition module in there before?
    If so? Why did you need to replace it?
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,631Member
    Yes. Sounds like the ignition module is bad
  • billtangbilltang Posts: 10Member
    edited February 6
    Thanks for all the feedback. The issue with this module is that intermittently it appears to unable to maintain 110v to the hot surface ignitor upon call of heat. Interestingly when it works, the red led diagnostic light also stays on. So I wasn't sure.
  • billtangbilltang Posts: 10Member
    Finally bought a replacement. It is slightly different with three tries instead one try (35-652505-003 vs 35-655600-003). It seems to work much better.

    Previously, the system works one out of about ten times at the worst case. Now it is much better, mostly ignites and stays on with the first try.
  • HVACNUTHVACNUT Posts: 2,041Member
    There should be ignition the first time, every time. Something else is going on there if it keeps losing 120v to the igniter.
    Check the pressure switches, hoses and their negative pressure vent and drain port bungs.
    Also check the drain itself.
    There will only be drain parts if it's a condensing furnace.
  • DZoroDZoro Posts: 752Member
    Igniters draw a lot of energy. Double check all main power wire connections. A loose or poor connection will cause issues. Follow the wiring right to the electric panel. The only thing on that circuit should be the furnace. If there is anything else that can cause issues. No lights, outlets or other.
  • Intplm.Intplm. Posts: 684Member
    Sounds like you might have a short or intermittent short. And as @DZoro said.
    Make sure this is on a dedicated circuit.
  • Jamie HallJamie Hall Posts: 10,284Member
    And while you are checking the wiring, check the ground as well. Often overlooked -- but you must have a solid ground back to the panel independent of the neutral.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • JUGHNEJUGHNE Posts: 5,579Member
    If the fire does not stay on all the time then:

    if you have a separate flame sensor rod, it may need cleaned.
    Also the burner must be grounded for the flame sensor to work.
    There may or may not be a separate ground wire for that function. Often the burner itself is assumed to be grounded.
    If wire is there check or reset each end of it for good continuity.
  • HVACNUTHVACNUT Posts: 2,041Member
    edited February 16
    Looking back, you never mentioned the make and model of the furnace.
    Also post a pic of the wiring diagram if you can.

    I recently serviced a 90+ furnace that was losing 120v to the HSI. Looked like someone erratically playing with a dimmer switch. Condensate backed up into the inducer fan housing and the water and fan were wreaking havoc with the vent pressure switch.
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!