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Lochinvar Knight KBN106, No 24 Voltage to Low Voltage Board

fieldguidefieldguide Posts: 7Member
I have no 24v low voltage to Low Voltage Board (causing a Gas Pressure Switch Fault & Lock). I have replaced both boards, the main board twice, believing the first must have been defective. Wiring connections have been checked thoroughly numerous times. On recommendation of an online Lochinvar tech, I've also replaced the fan. I have 120v at the main board, but no 24v coming out at the output connector. I bypassed the main board and supplied 24v directly to the low voltage board. By doing this, the furnace doesn't lock out until it wants to fire and then locks out, because of course, I have shut off the natural gas since other monitoring systems are not receiving voltage. With voltage into the main board, but no low voltage coming out, are there other possibilities besides main board? Thanks for any feedback!


  • IronmanIronman Posts: 5,309Member
    Did you check the low voltage fuse and transformer? The board doesn't create voltage; it receives it from the transformer.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • fieldguidefieldguide Posts: 7Member
    The KBN106 has a transformer dedicated to the gas valve only. It is working fine. 120 voltage is supplied directly to the main board which has its own voltage reduction and feeds the low voltage board. The fuses all check out. Thanks Ironman, other thoughts?
  • IronmanIronman Posts: 5,309Member
    Is this wiring diagram correct?

    If so, check for 24v between the terminals circled in green.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • fieldguidefieldguide Posts: 7Member
    Similar, but variations. Mine was installed in 2010. I have no voltage at any of the connection board terminals, which includes the room thermostat and therefore have no room temp display. Since there are no gas pressure switches, there is a jumper wire connecting the terminals. I'm getting the Gas Pressure SW Fault and subsequent Lock since there is no voltage here along with all other 24 v terminals.
  • fieldguidefieldguide Posts: 7Member
    Got it running!! Thanks Ironman for putting me on the right track!! I'm new to this site, so are there ways to credit you for all your help? Thanks again!!
  • JohnNYJohnNY Posts: 2,372Member
    Very cool, @Ironman !
    For installations, troubleshooting, and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is the Boilers and Hydronic Heating Systems Course Instructor at NYC's Mechanics Institute, a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
    John also oversees mechanical installations and maintenance for metro-area clients with his family's company, Gateway Plumbing and Heating along with his brother/business partner.
  • IronmanIronman Posts: 5,309Member
    So, what was the problem?
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • ZmanZman Posts: 5,334Member
    If you click on his post you can give feedback. Not that he needs more points :)
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • STEVEusaPASTEVEusaPA Posts: 3,494Member
    He needs his own theme song, like walk up music for the closer in baseball!
    Right now I’m hearing Black Sabbath's Iron Man...
    Daah daaaah dah dah dah
    Dah dah dah dah dah dah dah
    Daaah dah dah
  • fieldguidefieldguide Posts: 7Member
    @Ironman. I was studying my wire diagram after viewing the one you sent. I began tracing wires and realized something wasn't right. I discovered that 2 of the wire connectors were internally identical and therefore reversible. Mine were reversed! I was shocked that that was even possible! At any rate, the system is now good to go. Thanks for taking the time to help, you opened the way to solving the problem!
  • fieldguidefieldguide Posts: 7Member
    @Zman. Thanks for the help! (and friendly jibe :D)
  • fieldguidefieldguide Posts: 7Member
    @STEVEusaPA . Thanks for the laugh, you're hilarious!!
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