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Vaporstat sticking

I have a Honeywell mercury vaporstat that has worked flawlessly until I flooded my boiler to try to find a leak. I removed it and made sure the pigtail was clean.

What happens? The mercury switch gets stuck in the off position, but only at night when the system is off for the night. In the morning, the house is cold, I go to the basement and literally tap the vaporstat case so very slightly, and the mercury switch goes on. Then all is well for the entire day.

The vaporstat is level, as it should be. Is it OK to use a drop of oil or WD-40 to if that will help the pivot move easier.

Any suggestions?


Steve Garson
Newton, MA
Steve from Denver, CO


  • BobC
    BobC Member Posts: 5,477
    What have you got the vaporstat set at? They can get temperamental if you go too low.

    Water may have gotten into the vaporstat diaphragm, try removing it and see if there is any signs of water up inside the brass coupling. Try blowing air at the little hole at the base while holding the vaporstat upright - DO NOT USE AN AIR COMPRESSOR, a can of air would work as long as your careful.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Steve Garson_2
    Steve Garson_2 Member Posts: 712
    It's set at 6-oz, like it's been for over five years. Water in the diaphragm sound like it's worth checking out.
    Steve from Denver, CO
  • Steve Garson_2
    Steve Garson_2 Member Posts: 712
    Graphite lubricant seemed to do the trick.
    Steve from Denver, CO