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Knight High Limit Issue

Hvacman
Hvacman Member Posts: 159
in THE MAIN WALL
Pump off delay long enough? Have you purged HX lately?

I also noticed that a bad or intermittant F2 can cause this trip, you may want to replace the fuse and check it's holder.

PS, I love this boiler too.

Comments

  • Kevin O. Pulver
    Kevin O. Pulver Member Posts: 380
    I love these boilers! but help...

    KBN399 in a 15Kft commercial slab with 40 gallon Indirect.
    Often, Manual Reset High Limit (MRHL) trips out when indirect calls for boiler to drop other zones and full-fire on priority and then modulates down.
    I had Tech Support on phone and gave them all numbers from display menu. They confirmed all flow rates etc.. within parameters. They said MRHL out of calibration (non adjustable) and they sent a new one that worked for a few months but now it's doing it again. Display screen doesn't show high enough temp to trip, but MRHL trips anyway.
    (It IS the MRHL crying foul- Pull bulb out of well and it doesn't do it)
    Earlier MRHL had no reset button, you reset it on the touch screen. New one has red reset button, had to drill 1/4" hole between mounting screws for access to button.
    It tested fine but now acting up again.
    Only other difference in MRHLs I can see is they're made in different foreign countries. Has anyone had any problem with the MRHLs or got any advice? Thanks in advance. Kevin
  • G Averill_2
    G Averill_2 Member Posts: 48
    Knight KIT3086

    Kevin we have had a few of these KIT3086 manual high limits act up, as you are stating. When I visited the jobsites I noticed that this was actually occuring in the off cycle, just after a call for DHW, without a waiting call for space heating.
    What I did was to drop the maximun setpoint from 190F as I found it, to 180F, which was suitable for both of these jobs. This lowered the 'overun' if you will, to below the trip point of the manual reset. I also changed the system pump delay from the default of 30 seconds, to 60 seconds.
    I suggest that you review these temp settings as possible cures. Contact Aaron Liebhart in our Lincoln office if you need any additional help.
  • Paul Rohrs_7
    Paul Rohrs_7 Member Posts: 173
    Offset

    Kevin,


    Also make sure to check the programming for the Offset If the setpoint or target temp (with reset) is 195 with a 10°F offset, the boiler control will allow a 205°F temp and trip out your manual reset high limit which is adjustable but maxes out at 200°F.

    I believe the factory default is 9.9°F.

    Hope this helps.

    EDIT: Sorry, saw this is only on DHW.

    Paul
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