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KBN 285 fan

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EdFerris
EdFerris Member Posts: 11
edited March 2023 in THE MAIN WALL
My boiler locked out on Fan Speed last night. I had to replace the induction fan four years ago because of noise and vibration, which is becoming obvious again.  The old fan did have a defective bearing.  But the local shop that installs Lochinvar says they haven't had any problems with the fans.
If the fan does not rotate freely, there's no option except replacing it, right?  Anything that could be causing it other than a bad fan?  The intake is drawing air from the basement, so I know it's not blocked.
Edit: does anybody rebuild these?  If it's just a ball bearing, it would make sense to replace it.  The impeller does have two holes for a puller.  The local shop says they can't, though.

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  • hot_rod
    hot_rod Member Posts: 22,472
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    Do you still have e the old one to practice on? See what it takes to replace the bearings.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EdFerris
    EdFerris Member Posts: 11
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    Well, yes, I may have to do it myself.  Would like to know if other people have found electric motor repairmen who succeded.  New fan is $750; I'm used to paying around $100 for a fan.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,166
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    The issue with that fan is that it is designed to mix the fuel and the combustion air as it is fed to the combustion chamber. The motor must be of an explosion proof design. There are seals and gaskets that are not required for a simple motor that drives a fan that moves only ambient air. Second thing that increases the cost is the fact that it is a variable speed DC motor. There is a microprocessor inside the motor that communicates with the main control the operates the boiler. After the main control calculates the safe operation of all the parameters like temperature sensors on the supply and return piping, exhaust vent temperature and that the venting system is not sensing any blockage, the microprocessor in the master control communicates with the motor's microprocessor as to the correct fan speed for ignition, and ultimately the continuing adjustment of the fan speed needed to modulate the gas input to the combustion chamber based on all the temperature inputs

    Not just any simple fan motor.

    I would not want the responsibility of getting all that correct after disassembling that precision measuring device. Yes, a measuring device... the gas valve operates at a negative pressure at the outlet. The faster the motor rotates, the more suction the fan blade develops. The more suction there is, the more gas is expelled into the combustion air from the valve. That is how the variable input is achieved. Ramping the fan speed up and down adjusts the amount of gas and air is injected into the combustion chamber.

    Get a new factory built motor/fan assembly.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EdFerris
    EdFerris Member Posts: 11
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    Sure, I don't know the tolerances and whether I got them right.  That's one reason I'm asking here if anybody has done it successfully.
    I see the fan for the current KHB 285 is $450 instead of $750.  But they want the serial number of the boiler and where it's located!  Next step, you'll need a subscription to heat your house, I suppose.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,166
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    Serial number will determine when it was built. You certainly don't want the latest fan available if it is not going to fit the rest of the parts. Weil McLain is famous for changing parts on their boiler and calling it the same model number, with a different series. And if you get the control for the series 2 boiler it will not work on the series 3 boiler of the same model. I'm not sure about Lochinvar's KNB... but if you get the wrong part, you will not be happy when you get it home and find it won't fit.

    Have the Serial number available for the parts man!

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EdFerris
    EdFerris Member Posts: 11
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    Ordered a replacement fan from Supply House on Sunday, delivered Wednesday, installed Friday.  If I had known that the gas valve was not dismounted I would have installed the fan myself.  Fixed the problem.  Old fan does have a rough spot that shows a defective bearing.

    The tech noticed that the expansion tank was empty.  That may explain why I can't bleed my radiators.  Ordered that part, should be delivered this week.