Need advice on planning venting/pressure troubleshooting sequence

tate3441

We have a steam boiler system and our first winter in a ~1930s house we recently bought—this is my first steam system si apologies for dumb questions up front.  

Worked fine at temperate 50s outside, but as it has gotten colder, I think the pressure limit switch is preventing the boiler from turning on as often as the thermostat is ordering heat-on, and the house is pretty cold (set at 68, but I woke up and the temp was 64).

The system is currently set at 2.5 psi and I am reluctant to set it any higher with these old pipes and radiators.  My assumption is that this 1930s system has some clogged or inoperable vents throughout the system: either main vents along the main steam line or some of the radiator individual vents have failed shut.  Asking for the recommendation of the best sequence and methodology of my vent replacement, e.g., main vents or radiator vents?  Start at the end of the line and work toward the boiler or at the first main vent?   Do different vents have a different size orifice as I get further away from the boiler, or all the same size? Also, I am getting a lot of knocking and banging, and the pitch of all radiators and return valves seems good, so again assuming the vents are the problem with too much condensed water in the lines or radiators?

This plan to begin vent and steam valve replacement is based on my assumption that the boiler reaches 2.5 psi, some of the vents are not letting steam move along through the system quickly enough, then the house gets cold while the pressure switch at the boiler is waiting for the overall system to drop below 2.5 psi. I can see on the thermostat that the thermostat is calling for heat, and I have verified voltage is being properly received at the boiler control box, so I assume that it is the pressure limit switch that is keeping the burner from turning on periodically.  

EdTheHeaterMan

There is a great book for new steam heat homeowners https://www.heatinghelp.com/store/detail/we-got-steam-heat-a-homeowners-guide-to-peaceful-coexistence available in the bookstore on this site. You will want to read this one first. It will answer all your questions and some questions you didn't know you had.

Just so you know, the vents are more imoprtant than the pressure, as a matter of fact the lower the pressure the better. The Empire State Building is steam heated and runs on less steam pressure that your system is set. And I think your home in not quite so tall.

Locate the main steam vent(s) and make sure they are getting the air out and stop letting anything out when the steam gets there. If they don't let the air out, then you will not het any heat. Air and steam do not mix (like oil ands water) and air = cold, and steam = heat. So get the air out and you will have heat.

As long as there is any pressure in the boiler, (even just 0.5 PSI) there is steam in the pipes that want to get to the radiators. Move the air out and the rads will get hot.

tate3441

Many thanks.  Will order the book now.   How do I “make sure they are letting air out”?   Listen?  Or can I lift the relief with a screwdriver to be sure it is opening?   I presume this is the main vent.  In the room adjacent to the boiler room.

KC_Jones

Is this a one pipe or two pipe system? That matters as the recommendations can vary depending on the system. You mention radiator vents so I assume 1 pipe, but we've seen tons of 2 pipe systems that an unknowing tech added vents to.

tate3441

KC, many thanks for the response.  I just ordered the book so must admit I don’t know the difference yet.  Or presume 2-pipe is what I have: each radiator has a steam supply line and a condensate return line.  The boiler has big steam pipes out and smaller condensate pipes returning, so I presume a 2-pipe system.   Each radiator has a small bullet-shaped vent that I hear gently hissing at some locations.  The fact that the one in this photo has little dried rust trails at the top—does that suggest it has failed?  (Note: previous owner admitted a clueless tech overfilled the system when servicing prior to us buying the house, and that rust trail may have been water in the system—that tech mistakenly thought this was a hot water system and not steam!)

tate3441

Also wondering if the pressure cut-in switch is the problem.  I just turned it DOWN a couple of tenths from 2.5 to 2.3psi and the burner came right on.  Wondering if the internals get stuck after a while?

Jamie Hall

While you are waiting for the book -- a good read! -- let's start with the pressure. It's set too high. Fortunately, that's easy to fix. You have a nice standard pressuretrol, and there is a scale on the front -- and a little screw on the top. There is an index on the scale -- turn the little screw on the top so that the index is almost at the bottom of the scale.

Now you say... the pressuretrol will shut the boiler off before the thermostat is satisfied. That, it most likely, will. However, it should turn itself back on in a few minutes -- assuming that the thermostat is still calling for heat. If it doesn't, it may not be the pressuretrol which is shutting the boiler off. When the boiler shuts off with the thermostat still calling, what is the level of the water in the sight glass? The glass tube on the front of the boiler? If that is below the sort of vaguely triangular black box to the left of the sight glass, the boiler is waiting for the condensate to come back and that black box -- which is a low water cutoff -- keeping the boiler off until it does. The low water cutoff is supposed to work that way. The slow returning water isn't, and is something to be investigated.

I guess the point of all that is not to assume that it is one particular control when it might be another...

If that silver thingy is the only main vent you have, it is woefully inadequate. But we'll get to that...

EdTheHeaterMan

The main vents and the radiator vents will have air leaving them and if the system is properly designed, you will not hear the air leaving unless you get close to the vent itself. If the pipe or radiator is cold, and there is any pressure on the gauge, and there is no air leaving the vent, the vent has failed closed. A steam pipe gets very hot, over 200°F so you will know if the steam is there. If you still hear air leaving the vent when it is hot, then it is failed open.

There are 2 vents on your system. The main vent (or vents) are usually at or near the end of the main steam pipe that connects to all the radiators. They usually have a 1/2" or 3/4" pipe connection and are up between the floor joist just about 4" to 8" above the main pipe.

The radiators will have smaller vents and will connect about 1/2 to 3/4 of the way down the side of the last section of the radiator with a 1/8" pipe connection. There are too many vents to show them all but here are some common ones you might see available today.

tate3441

Jamie, the sight glass is showing about an inch below the stamped “full line” on the sheet metal chassis of the boiler casing.   At other times I have seen it higher, so the low water cutoff may be waiting for condensate to flow back.  

tate3441

Ed, the previous photo is of one of the main vents.  It is near the end of steam piping for one half of the house.  The other one I have seen in the floor joists of a crawl space way at the other end of the house.   The (poor quality) photo I posted earlier is of one of the little silver bullet vents at each radiator.   I presume poorly functioning vents will also slow the condensate return to the boiler, which matches the sight glass level I am seeing now (about an inch below the water fill line) so my symptom may be the boiler low water cutoff waiting for condensate to return, and not the pressure cut out?

Steamhead

@tate3441 , how long is each steam main, and what pipe size? This will tell us whether your main vents are adequate.

Also, are there two pipes connected to each radiator, or just one?

tate3441

Steam head, main steam lines are 2 1/2 inch OD pipes. There are two pipes for each radiator. Estimated longest run is about 50 feet.

KC_Jones

" 2-pipe is what I have: each radiator has a steam supply line and a condensate return line."

As a double check to this, are there traps on the condensate return lines? A picture of that connection could determine if there are.

IF there are, then you have 2 pipe steam and you shouldn't have any vents on the radiators. Those should all be removed. Now that said, most likely the system will work worse when you do that. So the next step, most likely, is to rebuild all the traps. At the same time that's going on the main venting needs to be looked at to determine how much and where it should be.

I'm not a 2 pipe expert so I would default to others for details, but on 2 pipe the radiators actually vent through main vents at the end of the dry return. This is why failed traps can cause a radiator not to heat, and the unknowing tech will add a vent which "fixes" the problem. What it really does is cover up the problem and potentially cause other issues.

tate3441

KC, many thanks.  I may be misinterpreting my description then and I may have a 1-pipe system.  Need to pull the wall covers off and assess what I have.

tate3441

Steamhead, I just left you a message to set up an on site con ULT.  I am in nearby Pasadena, MD.