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Which vaporstat

In looking up a part number for the Honeywell vaporstat, L408J, I see there are two sub numbers.  One has a SPST switch (L408J1025) and the other has a SPDT (L408J1009).  I didn't notice any other differences (are there?). 

For my one-pipe vapor steam heating system, which one do I want?

Thank you,



  • L408J Vaporstats

    Hi Mike- Here's some info on Vaporstats for you.

    - Rod
  • Luv'nsteam
    Luv'nsteam Member Posts: 272
    Vaporstat choice

    Hi Rod, thanks for the PDF's.  After looking at them, I think I want the SPDT vaporstat.  I think this because the vaporstat, LWCO (float) and LWCO (probe) will be wired in series.  The L408J1009 has the SPDT switch and breaks contacts R/B on rise, where the SPST only makes on rise.  SInce I am using the vaportstat to shutdown the boiler on pressure rise, and only the 1009 vaporstat breaks on rise, this is the model I want, correct?

    Thank you,

  • Steamhead
    Steamhead Member Posts: 14,838

    you'd use the other one to shut off the burner if the pressure fell. The 1009 is the one you want.
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Luv'nsteam
    Luv'nsteam Member Posts: 272
    Much appreciated

    Steamhead and Rod, many thanks to both of you for your help.

    Have a great week,

This discussion has been closed.