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[urgent] Is there a way to limit maximum firing rate for Lochinvar Knight boiler?

lkhelp
lkhelp Member Posts: 35
in Gas Heating

Woke up to a cold house and no hot water. Lochinvar Knight boiler starts up - the firing rate climbs up and then it shuts down at 98%. Repeat 5 times, then red lockout screen with "flame fail running" error. If I'm lucky - tech will come tomorrow, but it's c-c-c-cold!

I tried switching DHW type from Zone to Normal hoping that space heating demand will take over and it would use a ramp up curve that I have (which I can limit last stage to 90% for example), but it looks like DHW demand requires max firing rate regardless. I also tried to set SH/DHW Switching time to 0 and the other one to 15 min, and vice versa - but regardless - it still tries to ramp up to a 100%…

Thank you all!

Comments

  • hot_rod
    hot_rod Member Posts: 23,913

    the manual explains the many control functions

    IMG_0945.jpeg
    IMG_0944.jpeg

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • lkhelp
    lkhelp Member Posts: 35
    https://forum.heatinghelp.com/discussion/comment/1833357#Comment_1833357

    yes, i looked at those ramp settings, thank you. unfortunately for me, they only apply to space heating. when DHW heat comes in - the boiler tries to get to a 100% and i can't find a setting that would limit or override that…

  • Ironman
    Ironman Member Posts: 7,622

    You need to confirm that you’re getting sufficient flow through the boiler and indirect. A failing circulator or air binding can cause what you’re describing.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 11,204

    What problem are you hoping to solve by limiting the dhw firing rate? There are some legitimate answers to that but I don't see anything in your question to indicate that would solve your problem but maybe you have some information you didn't mention. If it isn't burning correctly, lowering the firing rate won't solve the problem. If there is some sort of issue with the gas supply then it could work around that problem temporarily

    That being said, you could turn off DHW, then it won't make a DHW call.

  • pedmec
    pedmec Member Posts: 1,145

    Your trying to make hot water that's why you don't limit the firing rate. As the boiler approaches 180 it will modulate down to try and maintain 180.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,910

    Possibly the issue has something to do with the indirect water tank or controls.

  • hot_rod
    hot_rod Member Posts: 23,913
    https://forum.heatinghelp.com/discussion/comment/1833398#Comment_1833398

    you can in fact change the temperature the boiler run on a DHW call. Factory default is 180, I don’t remember the adjustment range.

    If you had an indirect with dual coils, or a high output HeatFlo, you could generate DHW and tun low enough to condense.

    Same with adding an external plate HX. With a close approach HX design the B side can get within a few degrees of the SWT.

    Generate 120 DHW with 125 supply, for example. A plate HX is a much more efficient way to exchange temperature.
    It’s the key to the EK efficiency, the plate HX for DHW.

    IMG_0946.png

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    mattmia2GGross
  • HVACNUT
    HVACNUT Member Posts: 6,473

    This is old literature, but 4 tries and lockout, symptoms are the same.

    Screenshot_20250109_200834_Samsung Notes.jpg

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