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Furnace stops with front cover off

cotsy Member Posts: 1
Furnace runs intermittenly and does not keep up with set temperature. When the front cover is removed (not the blower cover) the furnace works fine. When the cover is put back on the furnace with stop (the burners go out). When the cover is removed, the burners come on almost immediately. It is a 20 yr old 90% furnace. thanks


  • VictoriaEnergy
    VictoriaEnergy Member Posts: 126
    Could be HX

    When heat exchangers crack open & fail, they do it gradually.  Could also be a clogged condensate trap etc, but a dying heat exchanger will do the same thing sometimes.  So for safety sake treat it as a serious issue.

    The 1st signs are often a very marginal lack of flow from the inducer, so the flame does not seem to be sucked into the heat exchanger as vigorously as it has in the past.  This might present in odd ways like runs only when you push the inducer to one side, or in your case the flame sensor instead of being completely immersed in the flame is lifting off and cutting out, and a little more so when the door is on.

    Do not operate the furnace until someone knowledgeable checks it out as it could be dangerous.
    Home Owners Please Note:

    You are receiving advice from some very skilled pros completely free of charge. One of the reasons I participate is to sharpen my own troubleshooting skills. So; did we get it right? I would be grateful if you extend this courtesy back by posting the final outcome of the issue you are inquiring about. Thanks
  • Empire_2
    Empire_2 Member Posts: 2,343
    I agree w/ Victoria Energy.

    If your 90%er is of 2 pipe construction, intake and exhaust, check you intake for any snow build up etc...  For the most part make sure there are no bows in the piping that may collect water and pool, causing a partial blockage.  If you have a differential pressure meter or magnehelic, there are measurements that can point you in the right direction.  I'll leave it at that until you get back to us.


    Mike T.
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