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Vaporstat PSI question

Clance
Clance Member Posts: 52
Hi Folks. I have 2 newly installed Magasteam MST288s in my 2 Family home. I noticed that the vaporstat on the boiler for system 1 is constantly at about 1.5 but the vapostat on the other boiler for system 2 is constantly at 0 even when hot - Both systems have about the same EDR not counting the 3 risers on system 2 up to the 2nd and 3rd floors. Both systems are heating fine. I did notice that system 2 had a drip on a rad valve that I rectified...(lost about 3/4" of water in the glass over a week.)
Why would 2 systems about the same size EDR with the identical boilers have such different vaporstat readings?
Should I be concerned about either?

Comments

  • Youngplumber
    Youngplumber Member Posts: 495
    What scale are you taking about here? Your vaporstat says 1.5 psi? 
  • Clance
    Clance Member Posts: 52
    edited February 21
    @ young plumber
    A picture is worth 1000 words...here's both gauges - 1-5 scale. Cool system when pics were taken.
    I see that the setting are different -





  • Youngplumber
    Youngplumber Member Posts: 495
    edited February 21
    OK I see. First off I wouldn't be worried about your observation. 

    Does the gauge reading 0 ever move? Like wiggle a little? What if you take it off and blow on it? Safely that is. Is there thread tape over the inlet? 
  • Jamie Hall
    Jamie Hall Member Posts: 15,350
    No reason for the two vapourstats to be set differently, is there?

    And the other comment -- that gauge which reads 1.7. Is that with the system cold? Is it connected to the boiler above the water line? If so, it's either busted or way out of calibration.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Danny Scully
    Danny Scully Member Posts: 1,319
    Have you calibrated the vaporstats to ensure they operating properly @Clance?
  • Clance
    Clance Member Posts: 52
    @Youngplumber
    @Jamie Hall
    @Danny Scully
    The system is cold. I took off both vaporstat gauges and blew into them and needles on both moved up but had to tap glass to get needles back down on both. System 1 was stuck at 1.7...after tapping 4 times went to 0. ... once reattached both stayed at 0 on the cold system...But I shouldn't have to tap the glass, should I?

    So I notice that both the vaporstat and Pressuretrol on system 2 are set higher than on system 1.
    See pics of each below.
    Pressuretrol Settings: System 1- Main 2, Diff 1.5; System 2 - Main 5, Diff is just under 1.5
    Vaporstat settings: System1 -Main 2, Diff 2.5; System 2 - Main 2.75, Diff 3

    I don't know why the settings would be higher on system 2 ...other than System 1 feeds a 1st floor apartment, system 2 feeds a 2nd & 3rd floor apartment... so the only real difference between the 2 systems is that System 2 has risers up to 3rd fl. - the rads up on 3rd fl get hot fast ..even with Maid oMist #4 on them... I had to pick up a couple TRVs to keep them cooler.

    I suppose one starting question is what should the vaporstats and pressuretrols be set at?
    And should the guages be sticking?
    Thank you !!










  • Youngplumber
    Youngplumber Member Posts: 495
    edited February 21
    They should be set as low as possible to make your house heat comfortably and evenly with "normal" cycling.

    Your using steam for its btu's. It doesn't need any pressure to give them to you and only a little to move throughout your sytem. 
  • Jamie Hall
    Jamie Hall Member Posts: 15,350
    Both vapourstats should be set for cutout -- main scale -- at 1.5 psi, both should have a differential (left hand scale) of 10 ounces (the figures you quote for differential in both cases are in mPa, by the way). Both pressuretrols should be set for 3 psi cutout, 1 psi differential. There is no need for them to be different. The elevation of the radiators makes no difference at all for steam heat.

    If a gauge needs to be tapped to return to 0 -- or to move -- it's busted. Junk it and replace it.

    You mention that you have TRVs on at least some of the radiators. Not good. The first thing to do is to get the venting correct so that the rooms stay close to what you would like. TRVs will not compensate for poor balance. If a radiator is heating too fast, the usual fix is to put a smaller vent on it. The Maid-o-Mist #4 is a slow vent, however.

    Could I ask what controls the two boilers? Independent thermostats, I hope?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Clance
    Clance Member Posts: 52
    Thanks again for your input!
    @Danny Scully - I wouldn't even know how to start calibrating the gauges, but would think the installer took care of all that :smiley:
    @Jamie Hall - Answers to your question - Yes, separate thermostats for each boiler.
    I actually had my system pretty well balanced after a week or so (not a big system) - I added 2 trvs to the 3rd floor because both my teenage daughters like their rooms colder and I couldn't go any lower than 4 on the Maid O'Mists.
    Looks like I should adjust the vaporstats and pressuretrols, take off the TRV and rebalance at the new pressure settings.

    So if both gauges are shot, (odd because they are both less than a month old) what might be a typical range I should be looking for them to show so as to know they are working.. for example - should they go up to like 1.5 when on and then back down to 0 when cold. Or do they pretty much hover around 0 all the time? Are there different brands of gauges that one is better then another? Thx again!
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 8,519
    @ Clance

    Before you possibly mess things up ask your installer if the vaporstats are set as needed. They may have set them and the scale on those can be way off. Also sounds like your low pressure gauge may be bad.

    I would put 1/4" petcocks or ball valves under the gauges them if not already there and leave them off only open them to check the pressure


    As far as your two boilers you do not need pressure on any gauge to heat a building. Your differences could be due to piping differences #of fittings length of run etc.

    If everything is working ok be happy
  • Clance
    Clance Member Posts: 52
    @EBEBRATT-Ed
    Thx. I emailed the installer and hope to hear back. The system that has been registering 1.7 on the vaporstat has less piping and a bit less EDR as the one with the vaporstat reading 0.
    I read on another thread that a vaporstat reading of 0 is actually a good thing as it means the boiler is properly sized...
    I do have shut offs under the gauge, I'll turn them off, and then when the system is running open them and see if they move...and then close them again -I'm guessing they should go back to 0 if the petcock is closed...if they rise and don't go back down to 0 when off that would be an indication if the gauge is bad, right? Anyway, the system is heating great -
  • JUGHNE
    JUGHNE Member Posts: 8,151
    Your petcock may capture and hold pressure when off.
    If you open when boiler is cool then they should go to zero.
  • Jamie Hall
    Jamie Hall Member Posts: 15,350
    They won't go to zero if the petcock is closed -- if the petcock is holding, they'll hold whatever they read when you closed it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
    Clance
  • Clance
    Clance Member Posts: 52
    @EBEBRATT-Ed
    @Jamie Hall
    I turned off the petcocks as suggested, and I set the system to Jamie's suggestion: Vaporstats main scale -- at 1.5 psi and a differential of 10 ounces. And the pressuretrol at 3 psi cutout, 1 psi differential.

    I guess my gauge isn't stuck at 0 as I thought... I cranked the heat up by 5 degrees and once the radiator valves closed the gauge went up to 1.5 and then boiler cut out, within about 45 seconds the gauge dropped to .9 and boiler fired. 2 minutes later it was at 1.5 and boiler shut off...45 seconds later it was at .9 and the boiler fired. I sat there and watched the same 2 minutes on/45 seconds off cycling for about 9 cycles then went and turned down the thermostat.

    So- I'm guessing the short cycling is not what I should be shooting for.

    My thought is that perhaps my vaporstat gauge never left 0 because previously the furnace never had to run long enough to heat all the rads and close the vents and therefore never built up pressure... rads were heating 3/4 of the way across and that created enough comfortable heat to satisfy the thermostat.

    I did hear back from my installer who said that is a trade off between the evils of short cycling and the evils of pressure/system optimization and the customers may not notice short cycling but will definitely notice any pressure issues- so he typically sets them a bit high and usually starts at 2lbs with a cut out of 1.
    He also said since I have a Vaporstat that the Pressuretrol is just a back up- so he sets it higher than the Vaporstat.

    So I set my vaporstat at 2PSI with a 16oz diff = 1psi I'll crank the heat tomorrow and time the cycles and see what's different.

    So now I get why @EBEBRATT-Ed keeps advising people that if it aint broke then don't fix it... and mine wan't broke :)
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 8,519
    @Clance Set the cut out at 2 psi and the differential as high as you can so the boiler cuts on just above 0. This will give you a longer cycle. As long as it doesn't cause venting issues it should work, you can always lower it to 1.5 psi if you have to In general lower pressure is better but 2psi should be ok.

    Maybe the installer can down fire the boiler slightly
  • Clance
    Clance Member Posts: 52
    @EBEBRATT-Ed - Thx. Sounds like you are on the same page as my installer. Just so I'm getting this... that would mean setting the vaporstat main @ 3psi and the Diff @ 16oz (Highest on the scale) = 2psi cut out?
  • Jamie Hall
    Jamie Hall Member Posts: 15,350
    The problem with 3 psi main setting -- other than burning extra fuel to get the pressure up there -- is that that is the maximum rated operating pressure of most vents. Not really a good idea.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
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