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weil mclain ultra 105 series 2 first digit 6

IZZY Member Posts: 52
Hi, I had this code last heating season. The boiler would start to heat for a few minutes, first digit 3 with the current water temp. After the temp rose a little, first digit went to 6, and then started a new cycle. This sequence would just keep happening (1,3, then 6, and back to 1) and the water temp would only gain maybe 1 degree each time. I did some research and it seemed that the supply/return sensor was bad. I changed the temperature sensor and that seemed to fix the problem.
I just turned the heating system on for the 1st time this season and it did it again, from a cold water temp around 75 and going up to 104, and then I got the 6 again. This time, however, after the heating cycle started again, it ran properly. Any thoughts? Should I expect the sensor to crap out again just to have it on hand in case it does? Since it happened two years in a row, I'm wondering if it might be some other issue causing the part to fail. Any ideas or experience with this?


    HVACNUT Member Posts: 5,478
    Have you checked and cleaned the igniter/flame sensor?
    When was the last time it was opened up and cleaned inside?
    How's the inhibitor level?
    Just a 6 could be flame failire, as indicated. The right tools will tell you why.
    All sensors can be checked using the ohms chart in the manual. 
  • kcopp
    kcopp Member Posts: 4,305
    May not be an issue.
    If the outdoor temp is higher...say 40F then the system high limit will also be higher. Do you have the outside temp hooked up?
  • IZZY
    IZZY Member Posts: 52
    first off- I apologize for not responding sooner, I thought I would get notified via email when a response came in and have been checking incessantly. I just now thought to log back in and see if there were any responses. 

    kcopp, the outside reset is hooked up, and outdoor temp was above 40, but I got the "6" on initial fire up, and then not afterwards.

    I will run it again once I change the expansion tank. the pressure went way up, just under 30, and don't want to run it until that is in check.

    hvacnut, thank you. I did a complete burner/ heat exchanger clean last year and it worked great all last heating season. I'll see if I can find the sensor ohm rating chart and check that out.