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Lochinvar WHN085

MikeJMikeJ Posts: 103Member
I'm an HVAC contractor -Steamfitter, put in a lot of Lochinvar boilers. Never any problems.
Had one sitting in the basement for 4 years.
Just put it in my house took out he muchkin boiler

Having problems, The first fault was going off on Outlet Sensor Fault, made sure no air in the system, Check sensor resistance
they check good, put in a new module (made sense) wrong!

Now getting Delta T high, again checked pumps, checked for air, ohm out sensors.

Now I notice before the boiler even lights my delta T reading is jumping all over the place, 6 to 35 to 12 to 20 -4 yes negative 4
Then the boiler lights within a couple secs, delta T jumps up out of range and locks out the boiler,

I already assume the module, we all know what assume means smiley:

Thanks for any help you may have



  • rick in Alaskarick in Alaska Posts: 819Member
    I am not sure if it uses the same sensor as the KHN, but they had problems with the temperature sensor on some of them. It is a four wire, duel sensor on the upper part of the tank. Apparently the wires did not get seated right in the manufacturing process and can get loose. I would look at changing that out.
  • DZoroDZoro Posts: 752Member
    Agree with @rick in Alaska , that would be a prime suspect. Had a few of those go bad.
  • MikeJMikeJ Posts: 103Member
    Yep I think @rick in Alaska nail it, restarted the boiler and apply some pressure on the Molex plug and was able to get the buffer tank up to 125 degrees. Then I must of a move and it locked out. Will wait for a few minutes and try again.
    Should get by till tomorrow don't have a sensor.

    Have another new Lochinvar sitting the basement from about 10 years ago, lol -not sure if they use the same sensor will wait.
    Thanks for the help
  • IronmanIronman Posts: 4,964Member
    Definitely sounds like the sensor. There are two thermistors in it and if they read more than 20* difference between them, the module will lock out on that code. We've seen the same issue.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • MikeJMikeJ Posts: 103Member
    Pick a sensor this morning and its working.
    The wholesale house did not have one, we took one out of a new boiler.

    There the Lockinvar dealer in town, Told me they have never sold that sensor before, all the way home thinking could i be missing something.

    Was very pleased that was the problem and its working.

    Thanks Guys
  • JUGHNEJUGHNE Posts: 5,579Member
    Ironman, are there 2 sensors in the same place/media so that a difference of 20 degrees will determine a sensor fault?
    Or is it a requirement of redundancy for limit controls?
    Or both?
  • IronmanIronman Posts: 4,964Member
    I’d say both.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • DZoroDZoro Posts: 752Member
    Scratched my head on that sensor (s) molex for a bit. Why they word it as a delta t difference, when the 2 sensors are in the same water, and the same molex. Just must be their way of determining that their main sensor has failed, because the 2 can't agree on the same temp.
  • Adolfo2Adolfo2 Posts: 31Member
    The Outlet Sensor failed on my WHN110 two years ago after having been in service for two years. Luckily I had a spare handy and I now keep TWO spares in the Lochinvar parts drawer.

    Not the best picture of the Knight display indicating the Lockout Condition but if you look closely...

    A rather interesting way (two thermistors in one sensor) of validating results for a mission-critical parameter. They do the same thing on the Flue Gas sensor.
  • MikeJMikeJ Posts: 103Member
    Putting pic to show the sensor,

    little surprised how small it is being two sensors and all.

    The yellow wire nut is for comparing the size to something.

  • NY_RobNY_Rob Posts: 1,368Member
    The actual thermistor component is about the the size of a grain of rice cut in half.. they're tiny.
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