Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Vent Dampers

unclejohn Member Posts: 1,830
I recently installed a cast iron boiler connected to a interior chimney. I have had to put the vent damper in the hold open position or the blocked flue vent switch will open. There is no other appliance on the chimney. It works and drafts fine with the damper open. Anybody else had this happen?


  • Tim McElwain
    Tim McElwain Member Posts: 4,588
    Yes I have seen it happen. Best solution is to move the vent damper closer to the chimney away from the draft hood. It will last longer there anyway as it is exposed to less heat.
  • unclejohn
    unclejohn Member Posts: 1,830
    edited October 2014
    Thanks Tim. Right now it is right at the boiler. I can flip the vent pipe around and put the damper on top, then it is one 90 and into the chimney. Do you think that 2' will make a difference.
  • Tim McElwain
    Tim McElwain Member Posts: 4,588
    It is worth a try. Either that or move the spill switch. I would have to see the installation to get a better idea of what would be best.
  • Robert O'Connor_12
    Robert O'Connor_12 Member Posts: 728
    Does boiler have a pilot or spark ignition? Had it happen once with standing pilot. The installer plugged the hole completely on damper. I imagine the pilot was enough for it to build up heat and migrate down and trip the spill switch.
  • j a_2
    j a_2 Member Posts: 1,801
    I think it must be electronic, ignition….I know in Maas. they are not even allowed to be sold with a pilot…Installed by there book I don’t feel this should happen….And I really don’t like the vent dampener, switched to open, and left that way…If you must, remove it and install a jumper…..Some may agree or not agree...