Two-Pipe Third Floor Radiator Slow to Heat

KarlW · January 14

Now that I have my system mostly functional with the last repair on the way, I still have a problem with the third floor radiator getting heat. Nearly all my forum searches on this forum relate to one pipe, not two pipe steam having this problem.

The radiator in question takes 45 minutes to heat or so, so unless my boiler is running for a long time, it doesn’t see any heat. My next slowest radiator (on the same main) heats in 10 minutes or less.

I know the radiator eventually works. When I have my thermostats set to allow the radiators to call for heat, it will bring this room to temperature eventually, but at the cost at ridiculous uptime and wasted heat on my boiler.

In my basement I have two what I believe are Hoffman 75s at the end of each of the steam mains, and they clearly let out air each heating cycle, and like I said, it’s just this radiator.

As the pipes run through the wall, I have no idea if they are insulated (and I am not going to rip open my walls to check), but experience tells me it likely has asbestos insulation - I have taken off the fiberglass insulation here while I diagnose it.

Any tips to get steam up here? Does an air valve up here make any sense?

Edited to add that the 2nd slowest radiator to heat is very likely a similar length of pipe from the boiler (just horizontal instead of vertical)

EBEBRATT-Ed · January 14

Looks like the trap is laying on it's side. No good. Disconnect the rad and raise it on blocks if you have to and re pipe the supply and return. And it looks like the trap is installed backwards

KarlW · January 14

@EBEBRATT-Ed These are side mounted traps - Illinois Engineering Company - I replaced this capsule and a bunch of others this fall - hence the shine on the cap.

These traps end up mounting about 1” higher or so (requiring a not quite-right awkward fitting) than a typical trap so capsule replacement is easier and cheaper.

Jamie Hall · January 14

How does air get out of your returns? That is much more important than how does air get out of the mains... Before you even think about throwing more vents here and there, find out how air gets out of the returns and vent that. Big vents. Then check the return from that slow radiator -- any bad pitch segments? Sags> It does go to a dry return, not a wet one?

KarlW · January 14

@Jamie Hall It could be ignorance on my part, but I don't see any vents on my returns at all, just the ones on the mains. To confirm this, where should I look?

Are two-pipe systems supposed to have air vents on the returns? As I don't know the answer, I didn't want to mention the apparent lack of them.

Jamie Hall · January 14

A two pipe system has to have vents on the returns somewhere. Consider: when air is being pushed out of the radiators through the traps, where does it go? It has to go into the returns. But then where? Actually, on the returns they could be almost anywhere, but the most common location is near the boiler, just before the high dry return drops down to the wet return and the boiler.

mattmia2 · January 14

It is possible this system has some sort of vapor device at the boiler that contains the vent or has the vent connected to it. Also could be up in dark corners of the basement covered with insulation or encapsulant or buried in a ceiling by someone who didn't know what it was. On some systems it was just an open pipe that often went outside or in to the chimney. The first step is to see where that return and the other returns go in the basement. Hopefully there isn't a part of the return in the wall that is pitched the wrong way and holding water.

The supply holding and water will slow or stop the radiator heating. The return holding enough water to block it will stop the air from venting and stop it from heating.

If i remember you said it would heat some if you cranked the pressure way up. That would indicate it is compressing the air enough that some steam can get to the radiator and condense. Once the steam condenses it collapses and pulls more steam in so insanely high pressure will cause a radiator that can't vent to heat some. I would look for the issue in the return being able to vent the radiator.

KarlW · January 14

I was out when I wrote the first few posts. But now that I am home, I can confirm that the vents are on the dry returns, not the mains - the first picture clinches it by showing the insulation on the other pipe - the main.

I have two steam mains and a Hoffman 75 on both of them.

As to more pressure giving me heat there - I’m less sure than ever. What I am sure is that at system pressure (cut-off at around 1psi) it takes a while to heat up, but does eventually heat up. It’s in the 20s today so the heat has been going quite a bit longer and it is working better.

KC_Jones · January 14

If those 75 vents are all you have I’m going to suggest you are under venting, possibly massively under vented.

I have more than that on my little one pipe system and it’s only doing mains. Yours are venting the mains and the radiators, so doing significantly more venting and significantly smaller.

How long are the mains and what is the pipe diameter? What is the system EDR?

KarlW · January 15

The mains are 130ft of basement branch, averaging 10ft of main per radiator branch I'd swag it at around 300ft. I believe my steam mains and returns are all 1.25in; they may be 1.5in. Branch pipe varies from 1/2" to 1" with 3/4" being the most common. All radiator returns are 1/2" to the 1.25" main.

The EDR is 748; this does align with my 250,000/205,000 BTU Boiler being slightly but not massively oversized (nominally 182,400 BTU at 240 BTU/EDR), if at all.

I also stumbled on this sizing paper on this site.

As I have Hoffman 17C and what I'll assume are Illinois traps (they likely aren't the same ones they measured) it appears that the Hoffman 75 is the limiter. Could it be as simple as changing out to Gorton #2s?

mattmia2 · January 15

in theory if the traps on the radiators are good you can remove the vent from the return altogether. You could leave it open for the start of a cycle at least as a test to see if it solves your problem.

KC_Jones · January 15

Something doesn’t make sense. No way on 748 EDR are the mains are 1.5 or 1.25 pipe. It’s got to be 2” at least maybe bigger. If it really is only 1 1/2 or 1 1/4, that could also be part of the problem.

And yes, you are massively under vented. I’d say you need at least 2 Gorton #2 vents per main based on the lengths you posted, maybe more. If the main pipes are properly sized, I’d say this venting is your primary issue here.

KarlW · January 15

@mattmia2 I am going to try taking off the vent for a cycle tomorrow and see what happens.

@KC_Jones Of all the problems I have, the one problem I don't have is an uninsulated main! I have a standard 4" header, and then I just looked closely in my boiler room, and it appears to be somewhere between 2 and 3 inches (I'd put my money on a 3" pipe, but there are a lot of joints) as it leaves my boiler room and goes above a finished ceiling. I can't see it through the encapsulated asbestos insulation when it is below the ceiling again. I assumed it was the same size as the end drop.

This thread has been very helpful to me, and I am likely going to a Gorton #2, it seems like less problems than a Big Mouth: https://forum.heatinghelp.com/discussion/187569/gorton-2-vs-barnes-and-jones-big-mouth

The big giveaway is that I hear hissing every cycle as @ChrisJ pointed out in the above thread, often even in the 2 minutes it takes to depressurize after a pressure cycle. I assumed it was expected (as have all of the boiler mechanics I've had over, but I've vented about that enough already), so I didn't bring it up here.

109A_5 · January 15

Hello @KarlW,

EBEBRATT-Ed said:
Looks like the trap is laying on it's side. No good. Disconnect the rad and raise it on blocks if you have to and re pipe the supply and return. And it looks like the trap is installed backwards

KarlW said:
@EBEBRATT-Ed These are side mounted traps - Illinois Engineering Company -

I'd like to see the documentation on that, sounds like wishful thinking. Once the trap closes, to keep the trap closed it has to open up the valve to let the steam in ? I bet that works well. The Steam, that comes from the radiator, is usually on the capsule side of the valve. Also I bet it works well when it fills up almost half way with condensate and it acts like a heatsink. The normal orientation of a common trap all the condensate just drains out the bottom. Maybe the capsule is special and expands at a much lower temperature than all the others do.

How many more are like this ?

This orientation may work better, no trapped condensate, but I still think the steam is on the wrong side of the valve for optimum operation. Thus letting too much steam into the returns.

KarlW · January 15

@109A_5 I have one other in this orientation in my main bathroom, and I can assure you that until it broke closed in the past year, the trap worked great, and this bathroom heated up relatively fast. With a new capsule, it heats up fast again.

The new pipework predates my ownership of the house (10 years or so).

Edited to add: I found another valve that isn't in a full-vertical position. This one also works pre- and post-trap replacement (I haven't gotten around to the repair yet).

As I look at it, a horizontal orientation shouldn't matter too much. It may drain slightly slower, but it would certainly open and flow properly out, especially if we are talking about that initial push of air through the trap that doesn't know which way is up or down.

109A_5 · January 15

Hello @KarlW,
I did not say you caused the problem, it's probably been an issue since the house had steam heat installed.

The point I'm tying to make is, for example, traps often fail open, this lets steam get into the returns and traps air in the system, this causes OTHER radiators, not the one with the bad trap to heat poorly since air is trapped in the system so steam can't get to that poorly heating radiator. Air that should be initially purged out, but is not due to bad traps. So you have pockets of air trapped in the system and the main vent may close prematurely.

When you have traps with the heat sensing device (the capsule) on the exhaust side of the trap's valve, the trap constantly has to open, passing steam to let the steam heat the capsule to keep the valve closed, brilliant. Seem to me this would make for a poorly preforming system, always letting steam into the returns from almost EVERY radiator.

The third floor radiator may have a significant amount of air to purge. If that air if is not purged correctly, how do you expect it to heat correctly ?

It also appears your system has at least some radiators that the supply and return are on the same side of the radiator. To me this provides a better path for the steam to get into the returns, since the steam does not have to pass through the whole radiator, just down one side.

Also it seems to me you can see where the condensate water line is most of the time. If this is the trap from the third floor radiator if may not matter much since it is not getting much steam anyhow. However the other one you found may be an issue. Heating that trapped condensate to get the trap to close may take much longer for the valve to close than it should, meanwhile steam is passing through.

mattmia2 · January 15

Could it just be a balance issue, you need to close the valves on the radiators that heat first some (or in the case of the TRVs all the way as a test) so that they start heating at more or less the same time as the 3rd floor radiator with has to vent all the air in the riser before it will heat? It needs to be somewhat in balance even without the TRVs for everything to work well. Maybe add some orifice plates to the radiators that heat first to slow them down a bit.

KarlW · January 15

So today I ran the system with the air vents out as @mattmia2 suggested.

This solves my short cycling problem and speeds up my heat on the third floor to acceptable but still slow levels. My boiler is now running from cold 20-30 minutes before shut off and longer during pressure cycling.

Judging by a water refill call today, I'm leaking some steam, but not massive amounts despite no vents. I have a Barnes and Jones Big Mouth coming Thursday, that I'll put where the Hoffman 75 was and put the 4A where the 75 was.

You can see the 4A spit water by the rust on top - this was a separate pressure issue.

My last step will be to try to get the pressure lower, maybe resurrect my vaporstat. The system sees equilibrium when heating at about 7oz so I'd like to set it there.

EBEBRATT-Ed · January 15

I don't see how those traps can work in those weird positions, but I am usually wrong anyhow.

mattmia2 · January 15

If steam is still blowing by the water seal even at low pressures, when it hits the vent it is going to close it and venting stops at that point. if it is hitting the trap in the radiator from the return it will also close the trap, feeling if the return at the radiator while radiator isn't heating will tell you if that has happened.

109A_5 · January 15

Hello @KarlW,

KarlW said:
So today I ran the system with the air vents out as @mattmia2 suggested.

Did you get any steam out of the opening where the 75 vent was removed on the return ?

KarlW said:
I have a Barnes and Jones Big Mouth coming Thursday, that I'll put where the Hoffman 75 was and put the 4A where the 75 was.

I think I would leave the 4A out of the system, use the Big Mouth and the 75.

With the Big Mouth make sure the valve seat "O" ring is seated correctly in the grove by looking into the inlet port. You may need a 5/8" male hex like an Allen wrench to install the spud properly.

KarlW · January 16

@109A_5 No visible steam, but I lost water (boiler refill) and thought I smelled water in the air. I realize there is some steam that leaks just before the traps shut, so I am attributing it to that.

It absolutely solved my short cycle problem so I am going to keep this going for a couple days, even at the cost of gallons of water.

I mistyped on the vent - the 4A is coming out and the 75 is going there.

109A_5 · January 16

Hello @KarlW,

KarlW said:
@109A_5 No visible steam, but I lost water (boiler refill) and thought I smelled water in the air. I realize there is some steam that leaks just before the traps shut, so I am attributing it to that.

It absolutely solved my short cycle problem so I am going to keep this going for a couple days, even at the cost of gallons of water.

Steam is easy to detect, use a mirror or a shiny metal object in the flow.

just so I am clear you just had the one vent on the return removed ?

I'm guessing with no vent to close to keep the steam in, your system will never build pressure, not really a solution. However the water loss and replenishment with fresh oxygenated water will shorten the life of the boiler over time.

mattmia2 · January 16

He only removed the vents from the returns. The vents in the returns should never close, if there is enough steam in the returns to close the vent there is another problem. in this case probably some steam blowing by the water seals but not enough to cause water hammer.

The height of the column of water pushed up in to the returns and down in the supply drips determines the maximum pressure it can build.

109A_5 · January 16

KarlW said:
Now that I have my system mostly functional with the last repair on the way, I still have a problem with the third floor radiator getting heat.

So the water seal drip (main to return) is presently still the same, not extended 8" down ?

mattmia2 said:
He only removed the vents from the returns. The vents in the returns should never close, if there is enough steam in the returns to close the vent there is another problem. in this case probably some steam blowing by the water seals but not enough to cause water hammer.

The height of the column of water pushed up in to the returns and down in the supply drips determines the maximum pressure it can build.

So removing the return vents that should NEVER CLOSE Magically solved the pressure issue ?

KarlW · January 16

It has not been lowered yet (the contractor had an emergency call when we were scheduled) I still have water hammer problems when the steam breaks the water line that hasn’t been lowered yet.

But, with the air vents off, the boiler isn’t pressurizing until it fills the radiators. Previously, it would pressurize from even a cold start, and the vents would hiss through many cycles before the air was released.

mattmia2 · January 16

109A_5 said:

So removing the return vents that should NEVER CLOSE Magically solved the pressure issue ?

In a properly functioning system. If steam gets in to the returns they will close, but steam shouldn't get in to the returns. They are there instead of an open pipe to keep steam from pouring out of the returns if some other problem occurs.

KarlW · January 16

Thankfully the steam is hitting the wet return and apparently quickly condensing while causing a lot of banging in the interaction.

It is not traveling up the Dry Return and I don’t think it will.

mattmia2 · January 16

If it is losing water with the vents removed and does not lose water with the vents in place that would seem to indicate the vents are closing against steam and keeping it from escaping.

mattmia2 · January 16

btw if you have a spare radiator trap around you can connect that in place of the vent.

KarlW · January 16

@mattmia2

I don’t think it is losing much water at all, I went to check on the water later and it appeared fine.

I do have a spare trap, but how do they compare to a Hoffman 4 or 75 in letting air out?

mattmia2 · January 16

They are usually much larger. The big mouth is just a steam trap marketed as a main vent.

KarlW · January 17

I had an exciting mishap tonight that allowed me to discover more.

Over the weekend, I removed the original 1920 doorbell transformer from my house. It was disconnected from power but had two cloth-insulated coiled cables that resembled phone wires. I disconnected these wires only to find that my boiler wasn't turning on.

It turns out that the original boiler must have had its thermostat connected to this transformer, and when the new boiler was installed, they connected the thermostat wire to the new transformer but left the wire running still connected to the old transformer! It gets weirder, but that's about what is primarily relevant here. After troubleshooting, I reconnected the boiler on Sunday.

Today, I came home from skiing in this 16ºF weather to find my house at 16ºC (60ºF)! I had a loose wire nut that took a few days to disconnect. I reconnected the wire, and the boiler now has to heat my house nearly 10ºF when it is now 15ºF outside, great chance to see it in action:

Some observations:

Good: The boiler did not cycle for quite a while due to pressure, only for low-water checks. This was nearly an hour, as all radiators were calling for heat.
Good: My open pipe air vents operated beautifully, and I am not losing water
Bad: At the end (after 3 hours of heating), when I was down to the last 2 or 3 radiators calling for heat, the steam line breached the water line and my severe water hammer occurred.
Bad: The third-floor radiator didn't get heat for about 90 minutes, along with two others. The weird part is their location and I'll elaborate below:

The three are my 1st Floor Living Room Front, 2nd Floor Master Bathroom, 3rd Floor Attic. The 2nd and 3rd Floor are close enough to be on top of each other, and the problem is almost certainly related. The attic is pictured at the top, and the 2nd-floor bathroom is pictured with the blue tile floor above.

The 1st-floor living room radiator is piped in series with at least four more first-floor radiators and likely four more second-floor radiators, all heated quickly. However, the 1st-floor radiator not heating is most likely the first radiator branch on the main (could be the second), and the 2nd-floor bathroom and 3rd-floor attic are likely the third or fourth branch on the main - I can't determine it with my finished ceiling.

It is also possible that in the case of the bathroom and attic, there is a first-floor radiator connected to the branch (the third radiator with a closeup of the trap), and the Living Room front radiator is directly below a bedroom radiator, heating quickly.

Any ideas on what would cause these to stay cool until after about 90 minutes of heating?

I can't speak specifically to the attic or first-floor, but the bathroom radiator used to heat quickly as recently as last year before the (now-replaced) trap broke shut and filled with water. I drained it when I replaced the trap.

mattmia2 · January 17

do those radiators heat quickly once they have got hot? if it shuts off for say 20 minutes then fires again do they now heat quickly? trapped water in the supply will kill the steam until the steam heats the water to steam temps. can you feel where the steam stops?

water can pick up sediment and clog up things or put dams in pipes that trap water but that doesn't seem likely here

note that if you don't have great main venting, 2 pipe systems can vent the main through the radiator and through the return pretty effectively

KarlW · January 17

The radiators heat quick once they get hot, but that's what takes 90 minutes.

They DO NOT get hot again after going cold unless the boiler is on for a long time.

The bathroom radiator in particular was heating fine until this year or maybe late last year when the trap failed closed and the radiator filled with water. On that note - it isn't just the radiator that doesn't get hot quickly, it is the inlet pipe as well - I'm not boiling radiators full of water, and when they get do get hot, it is steam hot, not just warming like it would be if I was heating water.

Here are pictures of the first-floor radiator which is NOT connected to the others.

mattmia2 · January 17

Trace the returns and see where they vent. Maybe they don't vent until water gets pushed through the water seal. Maybe that section of return inadvertently got isolated from the vents on the returns (or has a bad vent you don't know about). Alternately crack the union on the trap or the cover and open it and see if air comes out and stem goes in.

Maybe the bathroom radiator was heating because it was close to the boiler and you had the pressure cranked up so there wasn't a lot of air to compress.

Just a guess but it is easy to figure out if the issue is the air can't get out vs the steam is getting killed in the supply, harder to figure out why.

KarlW · January 18

So tonight I worked on the first-floor radiator. I couldn't get the cover off the MEPCO trap pictured above, so I took the whole trap off.

Hilarity ensued as water started spewing out of the radiator. After collecting it, I changed the trap to one that hopefully works. Turning on the radiator, the radiator did heat on the next heating cycle. I'll see tomorrow if the radiator continues to heat up or fill up with water.

If it doesn't fill with water, then @109A_5 may be correct on the traps. The traps may be able to be mounted sideways with the original bladder and open properly, but not with the Tunstall capsule. The other two slow radiators are the only two with a fully-side oriented trap.

mattmia2 · January 18

There may be an orientation to the new capsule to let the water drain too. Could be worth asking whoever you bought them from about the orientation, maybe they weren't aware that they were intended to mount on their side. Cracking the union over a pan will tell you if the other radiators are holding water.

109A_5 · January 19

Hello @KarlW,
If I had a house full of radiator traps, and I was maintaining them, I would make a setup to test them, probably near the boiler. Then you could prove how well they work or don't work in whatever configuration or orientation they will be used in. Test don't guess, right ? Some 11 videos here you may find interesting.

https://www.youtube.com/@barnesjonesinc.1225/videos

Reminds me of your situation.
Crossover trap installed backwards test

https://youtu.be/XI7uiHaT25U

EBEBRATT-Ed · January 19

I must be dumb, but I fail to see how those traps can possibly work correctly on their side.

KarlW · January 19

@EBEBRATT-Ed I can't answer the why, but with the original bellows they operated fine, with the capsule they don't appear to. But I haven't fully confirmed that - they do still kind of heat and they haven't been opened all winter (i.e. they'd be filled to the brim with water by now).

I've replaced the newer, standard orientation thermostatic trap on my first-floor radiator. Wednesday I replaced a bad trap with a bad trap, so I replaced it again last night (Thursday) and it appears to be doing better. I'm going away for the weekend so I won't crack the union on the horizontal traps until I return Sunday.

Two-Pipe Third Floor Radiator Slow to Heat

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