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High pressure boiler

I recently bought (moved in 4 days ago) a multifamily home. Each unit (one unit on the first floor, one on the second) has its own boiler and heat system. I've been doing some casual reading about steam heat to start learning about it. 

Today I got a text from the tenant that their heat was not turning on so I went to the basement to look at the boiler. A few notes:

1. The cut in pressure was set just below 8!

2. The pipes were all cold (so I assume had been off for a bit) and the pressure gauge for the boiler still read about 8ish. 

3. The water level was very low. 

While I was down there, I added water and nothing happened after that for about 10 min. As I'm checking things out, the boiler spontaneously turned on. What I assume happened was that the boiler pressure fell just enough to hit the cut in pressure so it turned on. 

So I know I need to do a few things. Obviously, lower the cut in pressure (which would probably solve the low water issues I've been seeing). But my main question is, could the high cut in pressure force this never ending loop where boiler comes on, hits cut out pressure but the pressure is so high that the air vents on the radiators stay closed and the system doesn't vent at all? And then when the thermostat calls for heat, the pressure is still above the cut in? Is that possible? 

Next, I don't have any main vents. Are those 100% necessary? Both units are only about 1000 square feet, so not big systems. Our second floor system seems to work totally fine. Every radiator gets warm, no hissing, when the boiler is on the pressure gauge reads about 4 and and the cut in is set to 0.5 (not sure what the differential is). 

And finally, I assume that someone on purpose set the cut in pressure to about 8. What are the reasons/ root causes that would cause someone to do that? Obviously someone who didn't know what they were doing and said here's the solution but didn't actually fix the problem. 


    EBEBRATT-Ed Member Posts: 15,540
    First of all no residential heating system should cut out at more than 2 psi, in fact a lot of systems don't build any pressure on a 3 psi gauge.

    Post some pictures of the system a radiator or two and the piping around the boiler.

    I would shut the boiler down, remove the pigtail off the pressure control and clean the pigtail , pressure control and make sure the gauge works. Also blow down the low water cutoff while the boiler is firing and make sure it shuts off the burner

    Main vents are 100% necessary, some old coal converted systems had few if any vents.

    Then I would make sure the radiator air vents all work (or replace them)

    And adjust the pressure control to cut out at 1.5-2 psi and cut in just above 0.

    That will get you started. @Dan Holohan has plenty of steam books available on this site

    And if you need a contractor to help you sort through this check "find a contractor" on this site
  • steamnewb
    steamnewb Member Posts: 5
    Thanks for your help. I'll post some photos tomorrow as the basement does not have sufficient lighting at night. 

    Could it be a coal conversion? The house was built in 1931, was oil at some point and is now natural gas. The boilers are both from 1982 (which is uhh older than I am). The gauges on the boilers go up to 30 psi which seems nutso.

    Anyway, my plan was to make sure all the vents work, lower the cut in and see what happens. I'll add in cleaning pig tail, checking the gauge and blow down the low water cutoff. Is there a way to test a vent other than just seeing if the radiator gets warm? 
  • SlamDunk
    SlamDunk Member Posts: 1,581
    edited December 2020
    Cant be a coal conversion if boilers are from 1982.

    The max allowable working pressure of the boilers are likely 15psi. Code says gage needs to be twice that. Lets you see if you have a runaway boiler.

    You might want to replace 15 psi pressure relief valves. They should have been relieving pressure.

    Second everything @EBEBRATT-Ed wrote
  • Jamie Hall
    Jamie Hall Member Posts: 23,323
    And I'll add a bit to @EBEBRATT-Ed and @SlamDunk -- you will want to make sure that the vents and any traps still work at all. If the boiler really ran up to 8 psi, they may be destroyed -- the maximum working pressure is 3 psi for most of them.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • steamnewb
    steamnewb Member Posts: 5
    Photos attached. Photos taken this morning when the boiler is not on.
  • PerryHolzman
    PerryHolzman Member Posts: 234
    I suggest that you also replace the pressure gauge with a new one after cleaning the pigtail. Old gauges often read incorrect values; and you really do not know what the steam pressure is.

    A similar thing can be said for older controls and relief valves.

    But, getting and known accurate gauge is the 1st step.

  • steamnewb
    steamnewb Member Posts: 5
    A lot of what was in my original post was all a red herring. I called someone to take a look. The pressure gauge was definitely crap. We turned down the cut in pressure, turned down the differential, cleaned the pig tail and then we jump started the boiler using the thermostat wires at the boiler. Worked totally fine.

    Later that night, tenant texts and says their heat isn't working. I go down, boiler is not on, I jump start it with the thermostat wires, it starts right up. So now I think the thermostat is the problem.

    I replace the thermostat and no dice. Replace again, nope. My wires don't read a voltage but there's obviously power because the boiler will turn on when the wires both at the boiler and the thermostat are touched. I also turn off every breaker and none control the boilers. I cannot find a transformer.

    Turns out my boiler has a power pile. Their thermostat was indeed going bad and intermittently working. The replacements we bought were not compatible with 750 millivolts. We purchased one compatible and the boiler fired right up. While there may still be issues with their boiler that we don't know about, this solved the main issue of it not starting when the thermostat called for it.
  • ethicalpaul
    ethicalpaul Member Posts: 5,704
    We've all been there in red herring land. Congratulations on finding your way out
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • mattmia2
    mattmia2 Member Posts: 9,664
    Are you sure that boiler isn't more like 1962? I guess it could be 1982, but it looks much older and a thermopile type valve on a new installation was not very common by the 80's.