Bringing a 2-pipe pumped-return steam heating system back in service

Jamie Hall

A few thoughts. First, on a true two pipe system -- which I think you have but I'm still not sure -- the pipe to which you are referring as a condensate return does do that, but is more correctly thought of and termed a dry return. This is important, as that pipe not only returns condensate, but is also the air vent for the radiators and, if there are crossover traps somewhere, the steam mains as well.

It has nothing to do with condensate pumps. If the traps are working properly and any drips -- drains or whatever -- are piped to a wet return at a level below the water line in the boiler, that pipe -- the dry return -- will always be at atmospheric pressure or only slightly above.

Basically, as the system fires, steam gets into the mains, which are vented usually by crossover traps into the dry return (which in turn vents to the atmosphere at or near the boiler; in some older systems it may be actually open to the atmosphere). As steam begins to fill the radiators, they in turn also vent to the dry return(s) through the traps. Condensate in the radiators also drains to the dry return through the traps.

Condensate in the dry return goes to a low point, and then down through a drip to a wet return. Air in the dry return goes, as mentioned, to the main vent(s( near the boiler.

The presence of a condensate receiver or tank at low level complicates things immensely, as if it s there there is nothing to prevent steam from coming down the drips to the wet return to the tank -- and also going back up a drip to the dry return. Neither is desirable, so there must be traps on the any drips from the steam mains. Usually F&Ts.

Presence of steam in the dry return (or condensate receiver) indicates that one or more of the traps has failed open; this must be tracked down and fixed before trying to fix anything else on the system.

All of this is true regardless of whether the radiation is standing radiators, baseboards, long fin tubes, or whatever. And they all in most systems need traps on the outlet and they all need to pitch to allow condensate to drain to and through the traps.

On venting -- no vents are required or wanted on any of the radiation. There are two possibilities for the steam mains: they may have main vents at or near the ends or they may have crossover traps (which are like radiator traps, but mounted above the steam main) connecting to the dry returns. The dry returns will be vented where they join near the boiler; this vent or vent cluster is the main vent for the entire system, and must be generous.

As noted above, if the steam mains and dry returns drip into a wet return which goes directly to the boiler and is definitely below the boiler water line there is no need for traps on the drips. If, however, the wet return is too high (above the water line) or as it is in you setup connected to a condensate receiver, there must be traps -- usually F&T -- on every single drain line from a steam main. It is worth adding, perhaps, that these F&Ts will not serve as system vents. You still need those.

JUGHNE

Assuming the steam main going into the crawlspace is running down towards the crawl space window, (is this the part of the system that is parallel flow?) then the "drip" for the end of that main (EOM) should run down hill back towards the basement.

Now think about how air will get out of either of those pipes....the F&T will stop the steam after it passes air to where??

The dry (high pipe) return will carry return water and air...that air cannot go anywhere because of the deep water loop seal of the wet return on the floor.

IMO, if the EOM drip was dropped down to the wet return in the basement, next to the dry return drop, that would stop the steam from getting into the high dry return pipe. (the F&T would no longer be needed).


But both of these drips would need an air vent before dropping down into the wet return. And both have to drop separately into the wet return.

Now, IF the traps on all the radiation served by that return were working correctly, there should not be any steam in that small return pipe, in theory you could vent the air with an open pipe.
If you did that you would know quickly if the rad traps failed as there would be a steam flow out of the open pipe.
I have purposely have done the open pipe vent on systems that have multiple dry returns so one can ID which section has failed traps.

Does this make sense?

PEvans

Big update: Working with a tech (not just me!) we bled the fuel unit and started the boiler. I really appreciate all the input here; I would not have been confident to do this in any other circumstances.

The burner ran for about 40 minutes, then stopped at the primary control and would not stay restarted. We ended up replacing the primary control and the ignition transformer. I had a new CAD cell so we put that in too.

The pressuretrol is a little sketch and seems to be sticking. It does not have a pigtail or local pressure display. If I have to replace it should I put in a vaportrol?

There is definitely steam in the condensate receiver, coming out of the vent. So I will go through the near-boiler F&T traps.

There are a few radiators that did not warm up even though their mains did. So those are probably individual steam traps.

Notably, this steam main section that we have been talking about did not warm up at all. So air is not getting out. I think as long as there is steam in the condensate receiver (and it is presumably seeing boiler pressure) there is little hope that this wet return will pass any air. Other thoughts?

JUGHNE

It is impossible for a wet return line to pass any air, unless you jack the pressure up to push air (and steam) thru the water seal. And jacked up pressure will wreck traps, both F&T and rad outlet types.

There has to be an air vent on the EOM before it drops down to the wet return. And if the wet return is below the boiler water line, that will keep the steam from traveling on.

Jamie Hall

If a radiator doesn't heat, but it's main and riser did, then either it's valve is closed or, assuming it has a trap, the trap is failed closed.

If a section of steam main has not warmed up, it's not vented (assuming that there are no zoning valves -- which is a whole different can of worms). There are only three ways a steam main can vent -- a main vent at the end of the main, a crossover trap into a dry return, also at the end of the main (possibly with a drip to a wet return, if the main is pitched away from the boiler), or through the radiator4s -- which last will be slow and uneven.

So... on that section of main, figure out how it is supposed to vent, and then figure out why it isn't.

As @JUGHNE said, there should never, ever, be steam in a dry return. That being a return pipe which is above the water level in the boiler, but not connected directly to a steam main. If there is then one or more radiator traps or crossover traps are failed open, and you need to find them and repair them.

F&T traps are used in some installations where there is a vented condensate tank. They should only be on drips from either a steam main or a dry return, and should discharge into a wet return. It is important to understand that an F&T is not a vent, and cannot function as one. Nor will it function properly unless there is some height between the main or return which it is serving and the inlet to the trap.

The steam you mention from the condensate receiver might be coming from a failed open F&T on a drip from a steam main -- not necessarily one near the boiler -- but could equally well be coming from a failed open radiator or crossover trap.

JUGHNE

If the F&T drip is after the zone valves, then you could try one zone at a time and possible narrow the steam source down as to which zone has the leakers.

This is only if the EOM's, are not tied together above the water line.

If they are then steam from one will pass into the other.

When you said some rads stayed cold, did you check both ends of them for temp?

Jamie Hall

Can we go back to square one here? Is this a two pipe system for sure? That is, steam main or mains, dry return or returns, and possibly -- wet returns?

If so, you must -- no options -- figure out which pipe or pipes are steam mains, which pipe or pipes are dry returns, and which pipes are wet returns. Then, having done that, the rule is very simple. Steam mains must be vented at their distant ends, either with main vents or with crossover traps. Radiators must be trapped or, if working on low and controlled pressure, have orifices or metering valves or some other widget to prevent steam from getting all the way through. All low points in either steam mains or dry returns have to be dripped to a wet return. All dry returns must be vented, either where they all join at or near the boiler or individually. If the drips go into wet returns which are directly connected to the boiler return, they don't need traps. If they go into a receiver, which I believe is your situation, they must have F&T traps if they are from steam mains, but they don't need F&T traps if they are from dry returns.

Now if you have zone valves, things get messier. The zone valves are needed on the steam mains They must be dripped on both sides of the valves, and those drips will need F&Ts if they go to a receiver, but not if the wet return goes to the boiler directly. If there are radiator takeoffs before the zone valve, they will need to have main vents or crossover traps on the main before the zone valve, just as if it were and end of main (which, when the valve is closed, it is). Dry returns do not need zone valves, but wet returns may if they are connected directly to the boiler and if the steam main is less than 28" for each pound of boiler pressure from the water line.

PEvans

The leg where the steam main did not heat up at all has baseboard radiators and a wet return. I misspoke (again) about the steam in the condensate receiver being related to this main not venting. I think the baseboards have venting if the manufacturer documentation is to be believed, and there is no other way I can think of for air get through a wet return; the designer seems to have been planning on water only. Right now the baseboards are hard to get to so I can't inspect them closely.

The two zone valves are dripped on the downstream side and the steam header is dripped on the upstream side. All of the radiator takeoffs are after the zone valves. Other than this one section of the main, all the returns are above the waterline and fall after an F&T trap to the condensate manifold and receiver; none directly to the boiler.

I can certainly test to see if the steam to the condensate receiver shuts off if I close a zone valve.

mattmia2

Jamie Hall said:

If a radiator doesn't heat, but it's main and riser did, then either it's valve is closed or, assuming it has a trap, the trap is failed closed.

Or another trap somewhere else has failed (or too high pressure or something else) is causing steam to get in to the return so that the air can't get out of the radiator and/or that steam is closing the radiator trap from the outlet side.

I suspect you will end up replacing all of the traps given both the neglect and the sitting unused for years but you want to make sure you only do it once, that you take care of any other problems that might damage traps before you do it.

Jamie Hall

"The leg where the steam main did not heat up at all has baseboard radiators and a wet return. I misspoke (again) about the steam in the condensate receiver being related to this main not venting. I think the baseboards have venting if the manufacturer documentation is to be believed, and there is no other way I can think of for air get through a wet return; the designer seems to have been planning on water only. Right now the baseboards are hard to get to so I can't inspect them closely."

Then that section -- the baseboards -- has to be treated as one pipe steam. Every baseboard must have a vent on it -- that will be immediately obvious if you get to look at them. You are entirely correct i saying that if they drip into a wet return, there is no other way for air to get out. It also sounds as though that steam main may not have any main venting -- and certainly not adequate main venting.

"all the returns are above the waterline " then those returns are dry returns and the must -- no option -- have main venting. The F&Ts, as i noted earlier, cannot be used as vents. Further, they are most likely superfluous -- those returns should never, ever, have steam in them and they should be at atmospheric pressure at all times.

mattmia2

PEvans said:

The pressuretrol is a little sketch and seems to be sticking. It does not have a pigtail or local pressure display. If I have to replace it should I put in a vaportrol?

A vaprostat would give better control than a pressuretrol. It has to be protected from the steam somehow. You could use a pogtial or you could make a trap out of tees and plugs. With the tees and plugs you can check and clean it without disassembling it by just removing the plugs.

JUGHNE

First, do you have a low pressure gauge (0-3 or 5 PSI) to show you what is going on?

New England SteamWorks

We see this all the time. The system was unbalanced, so some genius decided zone valves were the answer. Which then added the condensate tank as part of the solution. Which made everything worse, so system abandoned. If it were us we would recommended a new boiler (MegaSteam), ditch the zone valves and condensate tank, and return to original configuration. The likelihood of the original steam system being perfectly serviceable is extremely high.

PEvans

I'm now pretty sure that all of the mains are heating, even the one with the baseboards and the wet return. For sure one baseboard is hot. If there are issues it is with individual radiators -- stuck valves or closed traps.

Main #1 seems to put a little less steam in the condensate than Main #2. I have the Main #2 thermostat turned down so it will run less or not at all, and I'm trying to keep everything on to see what else I can see over time (I have replaced the ignitor, primary control, CAD cell, and burner motor so far, and it shut down on LWCO which seems to be at about 25% of the glass).

PEvans

JUGHNE said:

First, do you have a low pressure gauge (0-3 or 5 PSI) to show you what is going on?

No, unfortunately. I have the pressuretrol set about 1 psi differential and a little less than 1.5 psi cut-out, but I only have the big main gauge to tell me the pressure at any given time.

I'm not happy with the instrumentation.

PEvans

New England SteamWorks said:

We see this all the time. The system was unbalanced, so some genius decided zone valves were the answer. Which then added the condensate tank as part of the solution. Which made everything worse, so system abandoned. If it were us we would recommended a new boiler (MegaSteam), ditch the zone valves and condensate tank, and return to original configuration. The likelihood of the original steam system being perfectly serviceable is extremely high.

I have wondered about this from the beginning -- whether the condensate tank is really just related to the zone valves. My sense from this thread is that the lack of headroom, at least for this boiler with a waterline 21 inches below the steam mains, makes the pumped condensate a must. I would be happy to ditch the zone valves. I like the idea of TRVs at least in concept.

I am also thinking if I'm fixing radiator traps I will try putting Barnes & Jones internals in the 17C traps that are far from the boiler and/or on large radiators to help the balance.

PEvans

Should the burner keep cycling on and off, keeping the boiler between the cut-in and cut-out pressures, with no call for heat? In this configuration both zone valves are closed, and there really isn't condensing load other than the pipes themselves (and it gets good and hot down there).

Also it looks like the Main #1 zone valve does not close all the way, so that part of the house is getting heat all the time. These are Honeywell M644A actuators; I'm not sure about the valves themselves. Any tricks to work it closed? I might start a new thread on this.

Jamie Hall

Yes, if both zone valves are closed -- or partly closed -- the burner will have to cycle on an off to maintain pressure. What else can it do? It would probably save a good bit of fuel -- not to mention wear and tear on the burner -- to wire the system so that the burner will only if fire if one or the other zone valve (or both) is open.

Are these zone valves ball type (or plug) -- that is quarter turn -- or gates (or -- and I do hope not, globes)? It is remotely possible that the problem with the one not closing all the way is that the end switch in the closing direction on the actuator is misadjusted or faulty. You can take the actuator off the valve and run it both ways to make sure it actually goes both ways and stops when it should. Ball valves almost never fail, but if the do they have to be taken apart to replace the seal (which, in smaller sizes, isn't worth the effort). Again, though, you can check with the actuator off to make sure the valve does turn -- easily -- from full open to full closed. Gate valves if mounted with the stem up will almost always eventually fail to close completely. The only solution is to gain access in larger ones and clean out the track and the actuating screw.

In any case, take the actuators off and test them independent of the valve. Then start testing the valve by hand.

PEvans

Here are some pix.

The Main #1 valve is a 2-inch, the Main #2 valve is a 1-1/2 inch. They look like Honeywell branded gate valves. Both are nominally in the closed position in these pictures. The Main #2 valve seems to close fine. The Main #1 valve seems to pass some steam, enough to heat some radiators and bring the boiler pressure down so the burner comes on. To me it looks like the stem is discolored and there might be some further travel, even though the actuator is in the fully closed position. It looks like there might be some adjustment in the actuator.

Eventually I would like to replace both valves in function with thermostatic radiator valves.


Main #1 Zone Valve







Main #2 Zone Valve

PEvans

Jamie Hall said:

Yes, if both zone valves are closed -- or partly closed -- the burner will have to cycle on an off to maintain pressure. What else can it do? It would probably save a good bit of fuel -- not to mention wear and tear on the burner -- to wire the system so that the burner will only if fire if one or the other zone valve (or both) is open.

Thanks for your responses. I can think of an argument that says "save fuel and don't run the burner if no zone is calling for heat." I can also think of an argument that says "save the boiler and piping by maintaining everything within relatively small temperature and pressure range, avoiding any thermal shock to the system." Which is right?

mattmia2

The first one. If you are using the hot water in the boiler to make DHW or to run a hot water heating loop there is some argument to keep it hot at a lower temp with an aquastat for those loads, but if it it only for steam heating, there is no reason to fire the boiler unless one of the zones is calling for heat.

Jamie Hall

#1isn't closing all the way. No surprise there... you might be able to revive it if you took it apart. Might not, too.

PEvans

My system has a DHW loop that is no longer used and a wet loop for an external heating load that is not in service. So possibly it was wired to maintain pressure and now needs to be changed.

Thanks everyone.

JUGHNE

At this point FIWM, I would consider abandoning the zone valves at least temporally.
You can pull them up into the open position and clamp them in place with even a vice grips.

Then rather than throw money at zone valves, a few TRV's might be a more practical solution....not on every rad.
However this is just spinning your wheels until you get the entire system fired and figure out the main problems. Possibly trap elements at the rads.

You want to change all of the failed ones at one time.
A cheap FLIR viewer ($350-400) would show you the failed trap elements.

Do you have a low pressure gauge installed yet?

PEvans

Here is a potentially valuable reference for Honeywell valves:

63-7035 – Design and Application Guide for the Honeywell Valves and Actuators
https://customer.resideo.com/resources/Techlit/TechLitDocuments/63-0000s/63-7035.pdf

My actual zone valves are not here (in this guide), but I interpret them to be globe valves. The Main #1 actuator does not seem to move the stem much at all. Does anyone have any information on how the linkage is supposed to work? I can't even find a model reference for the linkage.

PEvans

JUGHNE said:

At this point FIWM, I would consider abandoning the zone valves at least temporally.
You can pull them up into the open position and clamp them in place with even a vice grips.

Then rather than throw money at zone valves, a few TRV's might be a more practical solution....not on every rad.
However this is just spinning your wheels until you get the entire system fired and figure out the main problems. Possibly trap elements at the rads.

You want to change all of the failed ones at one time.
A cheap FLIR viewer ($350-400) would show you the failed trap elements.

Do you have a low pressure gauge installed yet?

I have ordered some radiator trap replacement elements. I should be able to confirm or dismiss my belief that the all mains are heating but not all of the radiators are working due to trapped air.

If it still seems that there is steam in the condensate I hope I can identify bad F&T traps (or radiator traps).

I don't have a low pressure gauge installed yet. :-\

mattmia2

Remember that steam in the return because of a failed trap or other issue somewhere else will prevent the air from moving through that part of the return even if the radiator trap is good on that particular radiator.

PEvans

The doc I posted Sept 9 lists the returns that reach the condensate manifold. All of the returns coming from radiators have some radiators that heat up -- that is, despite what I said earlier, there are not whole steam mains or laterals that are not working.

I'm not sure I have the experience to distinguish between live steam and flash steam coming from the condensate receiver vent. When I get the gear together I will take a close look at each F&T trap with a surface thermometer and stethoscope, and perhaps I can determine which, if any, are passing steam.

I think having the cut-out pressure high-ish initially (over 2 psi) and half the condensing area air- or water-bound, making the boiler effectively way over-sized would make steam in the seem condensate worse. Is that right?

PEvans

@JUGHNE suggested a low pressure gauge.

Do you have specific suggestions on the installation? The picture below shows where it would have to go. The tap is on the side of the boiler, going to the main relief. There is a T, then the pressuretrol. I think the pressuretrol is turned because the wires are short; unfortunately seeing the control requires a mirror. Would I put in a vertical pigtail at the El, then T to the gauge and the pressuretrol? Does the orientation of pigtail matter given that the pressuretrol is a mercury switch? I might want to eventually put a vaporstat on this.

Also, I have not seen many 0-3 psi gauges. Amazon has some, with very mixed reviews. Grainger has one. 0-5 psi gauges seem much more common. Any specific recommendations?

delcrossv

There's a Winters 0-5 at Supply House for under $25. I'd go between the relief valve and the pressuretrol with a 1/2 x 1/4 tee, a brass nipple then a shutoff. then a pigtail up to the gauge. All straight up. Put a little water in the pigtail and done.

Jamie Hall

Yes, the orientation of the pigtail vs. the pressuretrol does make a difference when it's mercury (don't scrap it -- those mercury units are bulletproof, and if you put in a vapoustat for control you will keep the pressurerrol as your safety). The mercury units must be level, left to right -- and stay that way. Therefore, the curl in the pigtail has to be perpendicular to the font of the pressuretrol so that when it expands it doesn't rip the pressuretrol from side to side.

And related -- they are very sensitive to being installed out of level, which will affect the calibration of both the cutout and differential settings.

PEvans

Thanks, everyone. @delcrossv , no pigtail for the pressuretrol?

Jamie Hall

eh? The pressuretrol needs a pigtail, too.

delcrossv

Jamie Hall said:

eh? The pressuretrol needs a pigtail, too.

Yes, but there isn't one the the picture (???) Something unique to that model? Or just getting cooked?

BobC

On leveling the vaporstat it's important mercury vaporstats are leveled when hot. Pigtails move even when they are correctly oriented, just make sure it's level when it's hot. It doesn't make any real difference if it's a little off cold.

PEvans

If I put in a pigtail and T's that is a lot of surface area. Is there any concern with heat loss affecting what those instruments read?

KC_Jones

Low pressure gauge. I have the 0-15 ounce on mine and probably should have put something on my boiler with an even lower scale.

https://us.shop.wika.com/611_10_shop_en_us.WIKA?ProductGroup=89857&296=1222&298=1229

PEvans

@KC_Jones , that link had a 0-3 psi lower mount gauge also. Thanks. Either they are nice gauges or just really expensive.

Update: On delivery, really nice gauges. Swiss made and feel like a brick.

PEvans

The linkage for Honeywell M644A zone valve actuators with Honeywell globe valves is not well documented, so here is what I found out.

Lucky me, I have two zone valves, one of which (Zone #1) did not seem to operate. So I can compare working and not-working.

Here is Zone 1 (valve not working)


Here is Zone 2 (valve working)


In both cases the red highlighted piece rotates to move the valve. In the case of Zone 2, the highlighted piece moves the valve stem. In the case of Zone 1, the bolt in the middle had come loose, so when the highlighted piece rotates it doesn't move the valve stem. Comparing the two images you can see the displacement.

I tried a bunch of different things to get to this understanding. In the end, for the Zone 1 valve, I loosened that central bolt and used a hammer to drive the valve fully closed. I had been spraying PB Blaster on the stem for a while. This put the central bolt in a position more like that for the Zone 2 valve, so I crossed my fingers and tightened the bolt. Now the valve actuator seems to close the Zone 1 valve effectively.

PEvans

Low pressure gauge is in and the pressuretrol and relief replumbed.

Before:


After:


The clearance for the pigtail is less than I expected.

Here is an example of the cutout point. I have to watch it for a while to see how consistent it is. The pressuretrol got bumped around a bit when I did the work.