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Weil McLain ECO 155 Gas Boiler Constantly Cycling

np369 Member Posts: 3
I have a one year old Weil McLain Eco 155 gas boiler. It is constantly cycling through prepurge, ignition, heating (lasting about 10 secs), postpurge, prepurge, ignition..... every time it starts fire, it lasts only about 10 secs, and the flame signal is below 100, and then it shuts off the fire, restarts the cycle again.
We did exchange almost all parts (we have an identical unit next to it), and all parts seem function well.
At one point we took almost everything apart and put back, it worked for a while, but it returned to same behavior again. Since it constantly cycles through, I can smell incomplete burning gas smell from external exhaustion pipe.
Any advice would be very much appreciated.


  • JStar
    JStar Member Posts: 2,752
    Did anybody working on it have a combustion analyzer?
  • kcopp
    kcopp Member Posts: 4,188
    Is it LP or Nat gas?
  • unclejohn
    unclejohn Member Posts: 1,830
    Are you getting a error code? If not try bypassing the tstat and see if the boiler will run more then 10 seconds.
  • np369
    np369 Member Posts: 3
    Natural gas. No error code. Did bypass thermostat, no luck. Thx
  • unclejohn
    unclejohn Member Posts: 1,830
    Did you jumper the control at the boiler? No error code? It has to be the tstat!
  • np369
    np369 Member Posts: 3
    There is no error code except it shuts down and starts constantly. Not thermostat issue, we bypassed it when testing.
  • unclejohn
    unclejohn Member Posts: 1,830
    Try jumping the pressure control. I had a gas furnace that was doing a similar thing starting and stopping with no error code. Turned out the pressure switch was dropping in and out so quickly it did not register a error code. New switch solved that problem.
  • doitallmatt
    doitallmatt Member Posts: 1
    I had same problem w/ 3 month old Eco 155 this past week. According to Weil-McLain support, the problem is the the glue in original style burner gasket comes out and fowls up the flame sensor, causing the unit to shut down. The fix is a graphite burner gasket that will replace the original gasket (the graphite gasket will NOT be exchanged when installing an annual maintenance kit, you will keep the graphite gasket and toss the gasket that comes with the maint. kit). To keep the boiler running in the meantime, set it as an Eco 110 model.
  • Keitho991
    Keitho991 Member Posts: 1
    I had the same problem myself & I guess the wrong burner gasket has been installed at the factory on some Eco 155 models.
    The tech support people say the burner gasket needs to be replaced with a different gasket, supplied by Weil-McLain.
    For a temporary fix, you can go to "Contractor Menu", "Boiler Setting", "Boiler Model" and choose the "110" model.
    The Eco 110 model & the 155 model have different "flame signal shutdown" valves / settings.
    This temporarily solved my problem but the tech people say the correct gasket for the 155 must still be installed.
    Hope this saves somebody the headaches I occurred.
  • G Twitchell
    G Twitchell Member Posts: 9
    I have a similar problem as my 155 will not even light off, Fan short cycles 2-5 seconds and no gas valve or spark so no light off and this just continues