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WM Ultra 105 - Not reaching Target Temp

Chuck79 Member Posts: 1
I recently had a Weil McClain Ultra 105 boiler installed.  I have noticed on odd chain of events.

I have watched it cycle and I believe something is not right.  At start up it does the PrePurge, Ignite, and then fires correctly.  The burner will modulate as it should. Everything appears to be functioning correctly. However, when the supply & return temp difference is about 14 degrees the burner kicks off.  It then does a post purge.  Immediately it goes back to Pre Purge, Ignition, and then fires the burner for maybe 6 second and then the burner kicks off.  It goes back to post purge, then pre purge, then ignition and the 2nd time around the burner will fire and stay on until supply/return temp difference become 14 degrees.  Once the difference becomes about 14 the burner kicks on and we repeat, repeat, repeat.  It's the same exact cycle every time.  (at least for the few hours I spent watching it)  Given this it never gets to the 180 degree target temperature, it will only get to about 130 degrees max.

Any ideas?

Thanks for the help!

  Note:  Ground is good, ignitor is firing and looks strong, burner when on looks good and modulates, strong exhaust flow, no visible blockages on intake or exhaust, boiler pump and cirulation pump are working (just 1 loop)


  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
    it is not that cold out

    The boiler is most likely set with an outdoor reset that matches the boiler water temp to the heat loss of the dwelling, as in the cold the outside gets the warmer the water gets. this time of year 130 should be fine for most areas.
    Cost is what you spend , value is what you get.

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  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    edited October 2011
    My outdoor resets.

    It is 48F outside as I type this. I have a W-M Ultra 3 80. I have two heating zones.

    One is (oversize) baseboard, and if that zone were calling for heat (it is not), it would get 112F hot water.

    The other zone is radiant in a concrete slab at grade. If that zone were calling for heat (it is not either), it would get 79F hot water.

    Actually, the house is pretty well insulated and does not leak much, so neither zone has called for heat in the last week.

    I also have an indirect hot water heater, and the boiler is set to give 175F water when it calls for heat.

    P.S.: As far as I can tell, the U-Control displays the return water temperature, but I do not believe it uses it in its control algorithm, other than if the return temperature is much more than the supply, it faults. I have never seen mine do this. I have read that that mostly that happens if the supply and return sensors are wired incorrectly.
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