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Weil mclain ultra105

RicardoM Member Posts: 2
I have had this boiler since 2010, I have replaced the control board once and I do the yearly maintenance on it.
I'm having a problem that I have never seen before, my boiler works perfectly normal during a call for heat when my indirect is calling, however when my house thermostat calls for heat the flame comes on for about 8 seconds shuts off goes to post purge, then starts the pre purge, fires up and just keeps short cycling, no error codes, no red screen nothing.
Any thoughts?


  • RicardoM
    RicardoM Member Posts: 2
    If you read that post I put up, you can disregard
    I figured out the problem and it goes back to my Nest thermostat, for whatever reason it shows a call for heat but it keeps dropping it, so my boiler wasn't short cycling, my thermostat was but it wasn't showing it.
    I'm guessing the thermostat is crap.
    HVACNUT Member Posts: 5,858
    edited November 2018
    The Nest ain't exactly good.
    Did you connect the common?

    You also said you do the maintenance. Do you use the WM maintenance kit and tool to clean the HX?
    Who does the combustion test?
  • Leon82
    Leon82 Member Posts: 684
    I had a thermostat they would do that. It would call for heat for 30 seconds sometimes.

    I stuffed insulation above and below the hole in the wall cavity and also switched to a thermostat I could adjust the differential and set it tob1.5 degrees.
  • DZoro
    DZoro Member Posts: 1,048
    Nix the nest.... Let the boiler odr and control system do the work.