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Boiler not turning on

Hi -

I'm here with a repeat of a problem I had 4 years ago. (see

My boiler won't turn on when the thermostats are calling for it. There is a transformer box on the side of the furnace that, if I gently whack it, makes the flue damper open and the boiler will fire. The problem has been ok for 4 years but just started happening again.

Last time I was able to troubleshoot a loose wire inside, and I removed it from a connector and rewired it and it seemed to fix it. I'm kind of clueless as to what to check or how to fix it. Can anyone offer ideas? If I needed to have someone come for a service call, is this something a heating contractor can diagnose and fix or does it need to be an electrician?

Other suggestions from last time were to test the voltage on either side of the transformer and remove and clean the pigtails for the pressuretrol and LWCO. I never did those. I am sort of not sure how to. I have tried whacking the pressuretrol, but that didn't make the boiler fire. Whacking the transformer box did.

Any ideas? Thanks



  • Big EdBig Ed Member Posts: 869
    edited March 2014

    You would need a voltage meter to find the trouble ..Check to make sure you have 110 V AC between the white and black wires then check for 24 V AC between the yellow and blue... If you have 110 V in but no 24 V out you need a new 40VA or larger transformer . Could be a bed connection in transformer .. If you have both look further the circuit is mostly a series type but parallel through the stack damper and low water cut off , If you find voltage across controls or switches it will tell you that is where circuit is broken ...

    Better off calling in a heating service company , chances are he would have any needed parts in their truck ....
    I have enough experience to know , that I dont know it all
  • Steve WhitbeckSteve Whitbeck Member Posts: 669
    heating guy

    should be able to fix it.

    BUT if it does it again try tapping gently on the vent damper first. then tap on each component - you may just find out here the problem lies.
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