Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Knight KBN80 stopped working

Options
Boring
Boring Member Posts: 47
There was a message displayed on the panel that wasn't normal, but I don't remember what it said--nothing shocking though.....I powered down the system in hopes of resetting the system. When powered back up, the display is blank... Checked the 3 fuses on the board (in circuit) and they are OK.... I'm thinking the main board is gone---is this kind of "normal" for a 10 year old system? I did notice an "electronics" smell in the cabinet...hot/burnt smell but nothing shocking.... The other question is ---does one just replace the board or spend the money to replace the boiler? Looks like boards are 500 to 600 bucks...about 1/3 of the cost of a new boiler... Comments appreciated!!!

B

Comments

  • G Averill_2
    G Averill_2 Member Posts: 48
    Options
    Check the connections from the control board to the ribbon cable on the user interface control (display board) first. We do find some corrosion at this point, especially on an older boiler like you have. Clean any corrosion first. It is also possible that the display only has failed. This does happen from time to time. Hopefully the control board itself is yet in good order.
    Bob Bona_4
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    Options
    Concur. Had a bad ribbon or pin connectors on the mating ends on one.
  • Boring
    Boring Member Posts: 47
    Options
    service guys came out and replaced a board or two and adjusted some pressures...back in service again, don't know the costs yet. Now my pressure release is leaking at the boiler...maybe some crud in the seal/seat... cycled it manually a few times---have to see what happens, but it may be time for a new valve---seems like when they start to weep they rarely stop...at least that's been my experience on traditional water heaters....

    B
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    Options
    Bummer on the PRV. Double check the expansion tank is pressurized correctly and is the right size for the system, check boiler water pressure, feeder etc, before writing the PRV off to normal wear.
  • Boring
    Boring Member Posts: 47
    Options
    Floor is still wet from the Pressure Relief Valve leaking, but I did speak with the "boss" technician this morning. My wife was there while the work was being performed and she indicated some "pressure" was adjusted... I'm thinking they may have adjusted the incoming pressure reducing valve and may have added air to the expansion tank.... My system pressure gauge showed 40psi at one point and the PRV is a 30psi valve...

    The Boss Tech indicated Pressure reducing valves are a weak link...he wants me to close the ball valve ahead or behind the reducing valve , bump the PRV to release alittle pressure and see what happens over a few days... (this to test the reducing valve for leakage)

    What is the "ideal pressure" value I should be looking for in the boiler loop ? Minimum of 12psi(expansion tank charge) at room temp ... the "out" temp during a DHW cycle is 180°-ish that should produce the highest pressure/expansion/shortest pipe runs.... SH out is 150-ish --so if I get the pressure correct for a DHW cycle, there should be no problem during the SH cycles....

    Thanks for your comments.....

    B
  • NY_Rob
    NY_Rob Member Posts: 1,370
    Options
    The install manuals I've looked at indicate 12-15PSI as "working pressure" for common residential hydronic systems boiler loop.

    If the exp. tank is sized and pressurized correctly (and not waterlogged) for your system- you should see very little if any rise in loop pressure between hot and cold loop temps.
  • JUGHNE
    JUGHNE Member Posts: 11,075
    Options
    I have that boiler in my house and run the pressure about 15 PSI.
    I have a single story ranch. 15 would work for a 2 story IIRC.

    I do shut off the water valve ahead of the auto fill valve, however there is a low water cut off safety switch on the boiler piping well above the boiler. This is to avoid dry firing and overheating of unit.
  • Boring
    Boring Member Posts: 47
    Options
    Closed the ball valve on the exit side of the pressure reducing valve, pressure is below 30 now and so far the PRV hasn't shed any water...I suppose that points to a leaking reducing valve, or maybe the techs cranked it open more so the feed is feeding higher than 12psi....? Think I should turn the adjusting screw in a little and see what happens or just replace it with a calibrated 12psi valve? Also, what is the best way to measure pressure in an expansion tank? When the boiler loop has pressure, wouldn't pressure be present at the schrader valve on the expansion tank that includes the boiler loop pressure force? Would it be best to remove the tank and measure pressure in the "neutral state?
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    Options
    Bring the boiler down to 0 psi. Then check the x-tank pressure. Should match the systems needs with 0 psi on boiler side . In your case 12-15 psi, from the sounds of it. A pound per year loss is not alarming, from new. Turning in the PRV regulator screw will increase the fill pressure. I would not advise messing with it. Confirm your x-tank situation before looking at an overfeeding PRV.
  • JUGHNE
    JUGHNE Member Posts: 11,075
    Options
    Pressure reducing valves never get much exercise, for the most part they just sit there and never have to pass water.
    I have found for some that do not seem to regulate if the screw is run in and out they will come alive and work. Most also have an inlet screen to protect the seating mechanism.

    Turning the screw in will raise the pressure, other way will lower the pressure. Opposite of a water faucet.

    The air charge in the tank must be checked with absolutely no pressure in the system. If you can isolate the tank from the system and then loosen the tank to where you have no pressure on it then check the pressure. If you just take the tank off and no water comes out but you hear or feel water sloshing around in it then you need a new tank.
  • Boring
    Boring Member Posts: 47
    Options
    Pressure in the boiler system has been above 25 but less than 30 and have had no spills from the PRV--- Going to release more water this evening to get the pressure between 12 & 15 wait a few days and open the ball valve up after the Pressure Reducing Valve.... We'll see what happens....

    Thanks so far for all the suggestions / schooling--- this is a fantastic site---very informative...

    B
    Bob Bona_4
  • JUGHNE
    JUGHNE Member Posts: 11,075
    Options
    Do you have an indirect water heater? A pinhole in the internal heat exchanger could be raising your boiler pressure.
  • Boring
    Boring Member Posts: 47
    Options
    Since turning the pressure reducing valve off, my pressure has stayed consistent....I do have an indirect. I wasn't having any pressure releases until the tech replaced the main circuit board...not sure what else was done. I drained more water from the system tonight to get the pressure to 12psi. Have to monitor a few days to see if pressure changes, but from what I've seen so far I don't believe the pressure will rise... Just seems odd that this just started happening following the board change. The good thing is I'm learing more about my system. I'll keep ya posted.

    B
  • Boring
    Boring Member Posts: 47
    Options
    Going to replace to pressure reducing valve and the backflow device... The service guys took the backflow apart and reported a sticking poppet... I checked it out today and the poppet guide and spring do not operate smoothly at all...that, and knowing the PRV's fail often, I'm just going to go for it and see what the results are. In the beginning, it was the main circuit board that had failed. Maybe this will get me another 10 years!!

    B