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Weil Mclain Ultra 105 - b25 code

blee Member Posts: 5
I recently did a maintenance kit on my Ultra 105,
About a day or two later I started getting a b25 error message. It came and went, but every few days it showed up more frequently over the course of the last 2 weeks. Now I woke up this morning and the boiler wont stay on for more than a few minutes and is constantly showing the b25 code

Any ideas?
I'm a newbie, so I don't know any technical terms or abbreviations


  • blee
    blee Member Posts: 5
    (This is what I've found so far in the Weil Mclain Manual)


    Instructions in this supplement are based
    on factory default parameter settings.

    [Display flashes 9, then b in first position; last two digits on steady (code)]

    Outlet water temp rose too quickly - burner off for 10 minute wait (burner recycles, increasing wait 1 minute each attempt, to a max of 15 minutes)

    1 - Possible hot water return from DHW tank.
    2- Make sure system does not have trapped air preventing proper flow.
    3 - Inspect and verify system piping and components.
    4 - Verify piping agrees with boiler manual recommendations.
    5 - Verify proper circulator(s) operation.
    6 - Possible loose connector on boiler outlet sensor. Tighten connector.
    7 - Possible bad boiler supply outlet sensor
  • blee
    blee Member Posts: 5
    edited January 2019
    Another thing I noticed, when doing the maintenance kit, the cover plate that is supposed to be torqued to 50 inch lbs was hand tight. I took 7 of the 10 nuts off by hand which was kind of odd. When I re-installed the cover plate I torqued them to 50 inch lbs
  • blee
    blee Member Posts: 5
    Now it is throwing an E 36 code as well

    "Outlet water temperature sensor open circuit"

    1. Inspect outlet water temperature sensor and wiring.
    -Replace sensor if wiring correct and in good condition.
    -Replace low voltage wiring harness if problem persists.
    -Replace control module if harness replacement doesn’t resolve
  • DZoro
    DZoro Member Posts: 1,048
    Make sure all the connections that may have been disconnected are back in their proper places.
    Especially those two sensor wires.
  • Tom_133
    Tom_133 Member Posts: 796
    You probably broke the supply sensor, easy to do. They are cheap and available. Oh and you dont need to drain they just screw in.
    Montpelier Vt
    HVACNUT Member Posts: 4,336
    New sensors should have come with the maintenance kit. If it worked before you worked on it, then Occam's razor.
  • GW
    GW Member Posts: 4,418
    HVACNUT said:

    New sensors should have come with the maintenance kit. If it worked before you worked on it, then Occam's razor.

    what may I ask is Occam's razor?

    This is always a fine line-------"it worked before you came to do the maintenance...."
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • Tom_133
    Tom_133 Member Posts: 796

    I have never seen the sensors come in any kit. I could be wrong though happens all the time.

    383-500-300 thats the supply and return sensor part number.
    Montpelier Vt
  • blee
    blee Member Posts: 5
    edited January 14
    Well, I was searching for b25 error code because my boiler was throwing this code again. First result from google was this thread I originally created, lol. 

     Thanks everyone for your replies! 

    Also thanks to Tom_133, I just ordered a 383-500-300. Mine is falling apart and splitting in 2, after I seen this thread I went over to the boiler and pressed down on the sensor and the plastic cover snapped back in place and the boiler is up and running again.

    I was just about ready to start firing up some electric heaters 😅