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Lochinvar KHB - No DHW Priority

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Alan (California Radiant) Forbes
Alan (California Radiant) Forbes Member Posts: 4,663
edited December 2025 in THE MAIN WALL

Within the last week, there have been 2 customers with KHB boilers that have inadequate DHW and noticed that there is no DHW priority; both the heating pump(s) and DHW pump are on at the same time. When the heating is turned off, the indirect recharges like normal, but with thermostats calling for heat, it's a battle to the detriment of DHW, i.e. it never reaches setpoint.

I called tech. support and they suggested that it might be a stuck relay on the circuit board, but when I disconnected the end switch wires at the boiler, the heating pump(s) turned off.

Any input will be appreciated.

0-16.jpg
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

Two btu per sq ft for degree difference for a slab

Comments

  • plumbworker
    plumbworker Member Posts: 21
    edited December 2025

    How is the configuration set in the boiler controller for pump functions? dhw piped as normal directly off the boiler loop or piped as a zone off the secondary loop? When you disconnected the sh end switch the boiler pump cycled off? I take it these boilers have been in service for a while and this problem just started up?

  • hot_rod
    hot_rod Member Posts: 27,056
    Screenshot 2025-12-06 at 12.30.53 PM.png Screenshot 2025-12-06 at 12.32.44 PM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    plumbworker
  • 109A_5
    109A_5 Member Posts: 3,684

    Software bug ? Configuration not correct ?

    image.png
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,663

    @plumbworker The indirect is piped off the boiler loop and we installed the boiler in 2016; working fine since then.

    The DHW Mode is set to Normal.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • plumbworker
    plumbworker Member Posts: 21

    definitely sounds like a control board issue then.. when the end switch was disconnected did the icon for the boiler pump drop out? it should have if you have the pump function set to NORMAL.

  • 109A_5
    109A_5 Member Posts: 3,684

    Did you power it down, wait for a minute then power it back up ? Maybe the microcontroller just got glitched from some area brown out or utility switching event.

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,663

    @plumbworker Yes, when the Heat Demand wires are removed from the circuit board, the System and Boiler pump icons turned off.

    @109A_5 Yes, I powered it down a few times during troubleshooting.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • hot_rod
    hot_rod Member Posts: 27,056

    Something leaking from Livermore causing all these anomalies?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • plumbworker
    plumbworker Member Posts: 21
    edited January 11
    https://forum.heatinghelp.com/discussion/comment/1875912#Comment_1875912

    Alan, i'm curious what ended up ultimately being the fix on this job?

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,663

    Still no solution.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • tim smith
    tim smith Member Posts: 2,902

    Alan, try disconnecting power at wall switch or breaker, not rocker switch on boiler. Leave off for like 15 min, let capacitors fully bleed off. Worth a try. If not,copy all parameters down, then do factory hard reset. Wipe out settings and reconfigure. Just talked to my rep buddy, you have to have software to do hard reset. He could get it to you or your rep can with model/ser#. Not sure if will fix but???

  • tim smith
    tim smith Member Posts: 2,902

    you did go back into setup and verify priority is still on, correct?

  • plumbworker
    plumbworker Member Posts: 21
    https://forum.heatinghelp.com/discussion/comment/1881962#Comment_1881962

    Hmm, No dice from lochinvar? figures. Their "tech support" leaves much to be desired.. I'm thinking maybe if the boiler still falls under warranty you could at least try swapping the board.

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,663

    @tim smith Thanks for that hard reset idea. I'll contact the rep.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab

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