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Lochinvar KHN 110 Making Load, Vibrating Noise

Please help. It is o degrees here in Rhode Island and not expected to go over 10 degrees although my 2-year old boiler is working, it is starting to lockout after cavitating and making loud noises/vibrations. It pre-purges, post-purges, ignites, and sometimes locks out, saying that the fault is due to "too many recyclings." This is the second year in use, but a new problem this winter. The only difference I could offer is that it is brutally cold this week and I have the heat set higher than I did last winter, if that matters. The vibrations seem to be occurring more frequently and for longer periods. I am a homeowner and know little about these matters. I am waiting for a service call, but it is hard to get someone quickly in this weather.


  • If it is cavitation, that may indicate a low flow airlocked condition.
    Is there a working air vent on the system?
    What is the pressure of the system?—NBC
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    Too many recycling mean that it firednthen reaches temp limit because there’s no flow. Then cooked and fired again and so on.

    Pump is cavitation likely due to low pressure and/or air locked as mentioned.
    Gordyrick in Alaskahomeowner71315
  • homeowner71315
    homeowner71315 Member Posts: 2
    I took the advice someone posted a few years ago and stuck a $3.27 reducer over the 3" exhaust pipe outside the wall and would you believe, problem solved? I am an attorney, not a plumber or HVAC expert, but why couldn't Lochinvar tell me this when I talked to them last Thursday (before they took a 4 day weekend)?

    Now my question is whether or not my system will meet code with a reducer, and also whether any damage occurred over the past week when the boiler shook the whole house off its foundation with its vibrations? I could even smell gas near the unit a few times, which doesn't seem right. Why did it vibrate/howl in the first place? Is this "air lock"? The unit only has about seven or eight feet of 3" exhaust duct from the unit to the outside.

  • Boon
    Boon Member Posts: 260
    Is combustion air taken from inside the boiler room? The minimum combustion air and vent piping is 12 equivalent feet (page 16 of the I&O manual). Adding a reducer would effectively increase the equivalent length of your venting. A 90 degree elbow is 5 equivalent feet and a 45 elbow is 3 equivalent. I’m not qualified to say anything about the practice of adding a reducer.

    I have a 2015 model year KHN and from my experiences it sounds like you’re describing a combustion issue. Four or five failed/partially successful ignitions will throw a “too many recyclings” errors, and in my case the root cause was improper combustion.
    DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.
    EBEBRATT-Ed Member Posts: 15,517
    edited January 2018

    I would still have a qualified technician with combustion test equipment check it out.

    I don't claim to be a Lochinvar expert but most of the condensing boiler have minimum and maximum air intake and vent lengths. If you only have 7 or 8 feet of exhaust pipe it could be your issue and the reducer may help that. The Lochinvar manual should have the min and max lengths and elbow allowances

    Why didn't it happen before?? Maybe it never ran with weather this cold before.

    The amount of air a fan can move changes with the air temperature (colder air more dense, warmer air less dense) since air contains the oxygen used in combustion then combustion will also change slightly.

    Glad you were able to get it working
  • Ironman
    Ironman Member Posts: 7,376
    I agree that it's a combustion issue. The colder, denser air is causing the fuel to air mixture to lean out. You gas pressure could also be dropping with colder weather.

    The boiler should have been setup with a manometer and a digital combustion analyzer when it was installed. The I/O manual clearly details this and gives the acceptable parameters for combustion. You need to find a COMPETENT tech with digital combustion analyzer and have him setup the burner. The reducer on the vent is only masking the problem.

    Another thing that will cause a fog horn noise when the boiler is on low modulation is the use of CSST on the gas line. Setting the combustion to the richer end of the scale and/or enlarging or remove the CSST will cure that.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.