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Lochinvar KHB - No DHW Priority

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Alan (California Radiant) Forbes
Alan (California Radiant) Forbes Member Posts: 4,646
edited December 2 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: 16
    edited December 6

    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: 26,646
    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: 3,485

    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: 4,646

    @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: 16

    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: 3,485

    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: 4,646

    @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: 26,646

    Something leaking from Livermore causing all these anomalies?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream

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