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Weil McClain ECO 155 Display and Cycling issues

cpower Member Posts: 4
Context: Homeowner with some electrical and engineering experience

Boiler replaced with this new one 4 years ago, and has worked fairly well. Display screen stopped working 6 months ago (board burnt) but still worked fine so left it alone. Now it started cycling. Called a boiler tech out and he wouldn't work on it till the display was replaced. Tech is not able to come out again for 10 days and naturally I can't have a house without heat that long. So I ordered the display and had it shipped in as well as a new controller board just in case.

Plugged in the new display board, turned boiler back on at the service switch and then pushed the thermostat up beyond the current temperature. It's current status is prepurge and has been on that for an hour with the blower going, but it's not cycling like before. Screen is blue, no error codes on the main screen.

1. How long should prepurge last?
2. Is there anything else I should have setup as a part of rebooting it?
3. Is there a reboot sequence of some sort I should try?
4. Next steps?


  • Jamie Hall
    Jamie Hall Member Posts: 17,049
    Something's very much amiss -- prepurge should never be more than a minute, usually 15 to 30 seconds.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • cpower
    cpower Member Posts: 4
    So my next thought, looking through the manual is that I'm getting a zero from the flame sensor. When can ignition happen? Does it happen in or after prepurge?
  • DZoro
    DZoro Member Posts: 1,048
    You mentioned cycling before, have you checked your venting for blockage, drain system cleaned? Sounds like the boiler doesn't like what it is seeing during pre purge.
  • cpower
    cpower Member Posts: 4
    I'll look!
  • cpower
    cpower Member Posts: 4
    Took the condensate off the bottom and cleaned it out. little gunk but nothing stopping it. Fan is blowing full blast outside so I'm thinking the vent is fine too. Good try though
  • flat_twin
    flat_twin Member Posts: 291
    edited February 2019
    Default time for pre purge is 30 seconds. The fan speed increases during pre purge until it gets to 45% and then you should hear a click when the ignitor fires. Watch the diagnostic screen while it's firing, it will tell you exactly what the boiler is doing as it's happening.

    When was it cleaned and serviced last?