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vaporstat

Flip
Flip Member Posts: 40
ok, so new boiler install last fall good even heat but believe vapor stat took a beating over the winter. old Trane vapor system that seems to pull into a vacuum in the off cycle. was running around 1.5psi when it was originally started. now at 2.5psi with scale adjusted to the lowest set point. heats great but probably using too much fuel. could this be a vapor/vac system? and if so should the vaporstat be able to handle the vacuum it is exposed to in the off cycle?

Comments

  • Fred
    Fred Member Posts: 8,518
    edited April 2014
    Vaporstat or Pressuretrol?

    Do you have a Vaporstat or a Pressuretrol or both? When you say you are running at 2.5psi, is that based on a 0-3psi gauge or the standard 0-30psi that is typically installed on boilers? If you have a Vaporstat, the Main Scale should be set at 1.5psi (if that's where you want it and the Differential scale should be set at .1psi for a cut-in of .5psi.

    IF you have a Pressuretrol, they are set differently depending on if it is additive or subtractive Differential. On the additive, the white dial on the inside of the unit is set at "1" psi and the Diff scale on the front of the unit is set at .5psi for a cut-out of 1.5psi. For a subtractive version, the Diff is subtracted from the setting on the white dial. The real question here is does the boiler cut-out at 2.5psi and then kick back on once the pressure drops to the cut-in pressure? In most cases, the Vaporstat and/or the Pressuretrol don't engage unless and until the boiler pressure reaches those settings. On a normal heating cycle, you should only run a few ounces of pressure and never engage these control devices unless the boiler has to run for an extended period of time to recover from a deep thermostat set-back or unless it is very cold outside (like zero).

    If you are using a 0-3psi gauge on your boiler, it may be that the Vaporstat or Pressuretrol needs to be re-calibrated. If you are using a 0-30psi gauge, I would suggest you install a more accurate 0-3psi gauge before you attempt any adjustments. A picture of your Vaporstat or Pressuretrol would help a lot.

    One other thing to check is the pigtail that the Vaporstat or Pressuretrol is mounted onto. Is it plugged up with gunk? Take it off and clean it. If it is blocked, the Vaporstat can't see the boiler pressure. I know the boiler is new and you wouldn't expect the pigtail to be gunked up but the rest of the system is not new and gunk will return to the boiler.
  • Flip
    Flip Member Posts: 40
    vaporstat

    I have a vaporstat and a pressuretrol as backup . 0-3# guage. have not checked the pigtail as this is the first season .vaporstat is set at 6oz and differential is as low as it will go. unit shuts down at 2.5psi and on at 0 or below .i can hear the diaphragm in the vaporstat click when it makes the switch and can see this with a multimeter. just wondering if the vaporstat being exposed to a vacuum my have ruined it and if any one has seen this, can it be prevented?
  • Fred
    Fred Member Posts: 8,518
    edited April 2014
    Something's wrong

    Something isn't right with the Vaporstat settings. If you have the main scale set at 6 ounces and the Diff set at zero (as low as it can go) then you have no Differential and the Cut-in and Cut-out are both set at 6 ounces. I'm beginning to think that the Vaporstat is doing nothing (the micro switch is staying closed) and your back up Pressuretrol is actually cutting in and out on pressure. I would think you should set your Vaporstat at 12 ounces for the Main Scale and around 8 ounces for the Diff which will give you a Cut-in of 4 ounces and a Cut-out at 12 ounces. You aren't building enough negative pressure to damage the Vaporstat.
  • Joe V_2
    Joe V_2 Member Posts: 234
    edited April 2014
    I agree

    sounds like either a failed vstat or they are wired in parallel, instead of in series.
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