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.

Boiler Pressure Riddle

and mount it on a pigtail like the one the Pressuretrol is on. This will keep steam from hitting the gauge and distorting its internal parts.

I'd suggest getting brass pigtails for both the gauge and the Pressuretrol, these are much less likely to clog.

<A HREF="http://www.heatinghelp.com/getListed.cfm?id=367&Step=30">To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"</A>

Comments

  • Mark Gibson
    Mark Gibson Member Posts: 21


    In a nutshell: Why would a steam boiler indicate 15-20 psi when running, but not blow off the relief valve or shut down on a Pressuretrol set to 2 psi cut-in with a 3 psi differential, AND without shooting lots of steam out of a radiator with the vent removed?

    More details:

    I just moved into a 1700 S.F house built in 1924, with an oil-fired dry-return steam system with coil hot water. (Picture attached.) Walking by the furnace the other day I was surprised to see the gauge reading 17 psi!

    The next time the boiler fired from cold, I kept track of what happened: The pressure started at zero, and over several minutes slowly climbed to about 15-20 psi. (The gauge is definitely PSI.) Every few minutes, I briefly tripped the 15 psi relief valve's lever. Nothing came out until the gauge read 15 psi or so. At that point, steam (and water droplets) flowed out at a healthy rate, although not as much as I’d imagine 15 psi steam through a pipe that size would go. And the lever wasn’t much easier to move at 15 psi than at zero. If there were really 15 psi behind it, I’d imagine it would be really easy to move the lever. Also, the gauge didn’t budge when I did this.

    As a rough test of the pressure in the mains, I shut off the first radiator that comes off the main and removed its vent. Then I opened the hand valve again. While the burner was running (at an indicated 15 psi), air very gently flowed out of the hole – not fast enough to blow out a match. I tried this on two different radiators.

    Fast forward to the end of the firing cycle: The burner shut down (on thermostat, not pressuretrol) and over several minutes pressure on the gauge began to fall. I tried tripping the relief valve every now and again, and by the time the pressure dropped to 10 psi or so, tripping the valve released nothing at all. But after an hour or so, the gauge did in fact go back to zero.

    Other details: About 1/3 of the radiators are turned off. The remaining radiators don’t spit, hiss, or hammer. The system isn’t particularly well-balanced, but there are no main vents so I figure that plus the switched-off radiators are likely causing this. The water level is at the manufacturer’s level, about the middle of the glass, and it rises and falls within about a ½” range while the boiler is firing.

    At first I figured I just had a bad gauge. But if that were the case, wouldn’t tripping the relief valve (after the burner was off for a while) bleed off the pressure and make the gauge reading drop?

    Does anyone have any idea why the gauge would act this way? Is there 15 psi somewhere in the boiler, but not at the port for the blow-off?

    Thanks for any and all help!
  • Bad steam gauges

    The gauge looks like it is mounted directly into the boiler and in most cases these gauges get damaged over time because the water in the boiler rises and falls while boiler is operation yto produce steam for heating.

    Typically the gauge should be mounted out of the boiler line. To do this you will need to install a nipple and end elbow into the boiler tapping. As Steam Head stated install a pig tail (syphon tube) to protect the gauge, use brass fittings as these will not clog with rust.


    jake
  • Mark Gibson
    Mark Gibson Member Posts: 21


    Jake & Steamhead, thank you both very much for your help.

    I understand the use of brass and the pigtail siphon. (The gauge is marked "internal siphon" but obviously it wasn't enough.) So I know to use one with the new gauge.

    Jake, pardon my ignorance but could you elaborate on mounting the gauge "out of the boiler line"? My interpretation is that you're suggesting I run a nipple off of the hole the gauge is in now, then a 90° elbow pointing up, and then a straight pigtail running vertically with the gauge on top. As opposed to using a 270° pigtail like my Pressuretrol uses. If so, is this to get the gauge higher above the waterline? Or did I misinterpret?

    Thanks (again),
    Mark
  • Rich W
    Rich W Member Posts: 175


    Looks like a tempering valve below....Maybe DHW or hot water heat running through a coil in the boiler...Maybe you should be looking for the reason that you DON'T have 12- 15# all the time like you should. Is there a circ connected to the lines coming out of that coil? Where do those lines go?
  • Mark Gibson
    Mark Gibson Member Posts: 21


    Hi Rich...yes, those lines are DHW heated through a coil in the boiler. Cold water in, hot water out (via the tempering valve), and then off to my faucets. No hot water heat anywhere in the house, and no pumps.

    Thanks,
    Mark
  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398


    Mark is there any chance your gauge is masuring OZ of pressure and not lbs? Usually gages fail stuck or low. and it seems you have determined that you really do not have 15 psi. Just a thought. 15 oz is just less than a pound.
This discussion has been closed.