Question about my single pipe steam system: strange sound occurs only if boiler runs 30+ minutes

Alexnyu10

Good morning,

I have a 1920 home with a single pipe steam radiator system (6 radiators).  We have a brand new boiler installed one year ago.

we are having one strange issue that I am hoping the wisdom of this group can answer.

if the boiler runs for 10-20 minutes, the system heats up great, all the radiators get nice and hot and nothing too loud.  If I keep the thermostat set at a single temperature, the boiler will kick on for 10-20 minute cycles when needed and keep everything great temp. 

Here is the mystery:

If the system runs for 25-40 minutes continuously (this rarely happens, only if we let the house get colder to 60 degrees and then set the thermostat to 70 degrees will the boiler run that long continuiously while the house is heating up), after about 25/30 minutes of the boiler running continuously we begin to hear a air or steam hissing sound underneath the radiator (under the floor) at the farthest end of the house from the boiler on the main level of the house (boiler in basement but no radiators down there). We don’t see steam visibly, but it sounds like underneath the floor air or steam is releasing in a continuous shhhhh or hiss.  This sound ONLY occurs if the boiler runs continuously for about 30 minutes, and then if the boiler goes off the sound goes away immediately.  I have gone into basement with a flashlight right under where this happens and see no steam or signs of water under the spot, and honestly can’t hear the sound from the basement even thought you can hear near the floor at the furthest radiator on main level.

What could possibly be causing that sound to occur exclusively after the boiler system has been running continuously for 30 minutes? I tried to show my plumber once but the sound takes so long to occur that we missed it when he was here, he has checked and tuned up the boiler and the radiators themselves. 

Should I just keep my thermostat set at 70 so it never needs the boiler to run longer than 10-20 minutes, or is it okay to let the system run longer by using a thermostat schedule where it goes down to 62 overnight and heats to 70 in morning and just ignore the sound? 

Thanks so much, I love this group for steam wisdom. 

dabrakeman

Increased pressure can occur as the boiler runs longer and radiators start filling particularly if the boiler is oversized. What do you have your pressuretrol set at? Should set it at its lowest setting (cut-out 1.5psi / cut-in 0.5psi). Make sure the pigtail is clean as well.

Is there a main vent at the end of the main about where the noise seems to be coming from? Maybe it is stuck open.

AdmiralYoda

When my boiler water gets exceptionally dirty I will get some surging when it runs for an extended period of time. My near boiler piping is less than perfect.

Multiple pictures of the boiler would help, including the near boiler piping, the pressuretrol setting, and the site glass. If you have oils remaining in the system it could also make this happen. When a new boiler is installed it needs to be skimmed multiple times to remove the oils from the boiler.

pedmec

I'm of the opinion that you have a bad main vent. Follow the piping in the basement to that location. You should see a vent at the end of the supply main. Its probably just taking longer for the pressure to build up enough in the system for you to start hearing it.

Alexnyu10

Here is a picture of the current pressure settings when the boiler is off, very curious if folks think this is set right. Also for context the 3 radiators in upper level are turned off completely, so this is to power the 3 radiators on the main level that are open. It’s a brand new slant fin boiler GXHA-100 EDPZ

Alexnyu10

Alexnyu10

Alexnyu10

dabrakeman said:

Increased pressure can occur as the boiler runs longer and radiators start filling particularly if the boiler is oversized. What do you have your pressuretrol set at? Should set it at its lowest setting (cut-out 1.5psi / cut-in 0.5psi). Make sure the pigtail is clean as well. Is there a main vent at the end of the main about where the noise seems to be coming from? Maybe it is stuck open.

Based on this pic do you think it’s safe for me to lower that to the lowest pressure setting? Is it just as simple as pressing that little tab down? My plumber set this all up originally so just want to make sure before I tinker, but it’s definitely not on the lowest setting currently and that seems like a potential solution. 

Alexnyu10

Also one other potentially relevant detail. We had the near boiler piping in the walls completely replaced with brand new pipes when we did the boiler (not the entire system but the pipes close to the boiler in basement walls). 

Also when I try to locate the main vent I don’t see anything, all of the pipes in the basement are wrapped in insulation so I can’t specifically locate any vent. If the main vent is the issue (I am hoping the issue can be corrected by adjusting the pressure lower), how complicated is a main vent repair? 

neilc

when you hear that whistling,
how high up does the pressure gage read?

and where you think you're hearing that whistling, are there any pipes poking up thru the ceiling right about there?
post a picture of that area,

the Ptrol is set too high,
do NOT push on the tab, it's just an indicator for that scale,
on top of the grey cover there is a screw, turn it counterclockwise (loosen) and the tab should lower in the scale,
try to set it all the way to the bottom,
the screw adjustment should turn easy, til it doesn't,
do NOT turn past that initial resistance or parts inside could fall apart,
this should put you down on the scale to about 0.5, for a cut in setting,
loosen the front cover screw and lift the cover off after shutting the boiler off at the safety switch,
inside should be a dial, set the dial so the number "1" faces forward,
this is your cut out differential, and boiler should shut down at about 1.5 psi,
turn boiler back on,

if by chance boiler does not restart on a call for heat, and gage is reading at 0,
it's possible you may need to turn the main scale screw clockwise (tighten) to raise the indicator just a bit, try one turn, or a half, at a time till boiler restarts, and restarts reliably if it's needed,
you want to run the Ptrol as low as reliably possible, 0.5 cut in, 1.5 cut out, boiler should not need to be above 2 psi, ever

Let's find the main vent and then we'll figure out the difficulty facture,
but it's basically unscrew the old one, and put a new one in place

Alexnyu10

Alexnyu10

Just did gentle counter clockwise to get it to bottom and also made sure the number 1 was facing forward like pic above, will keep you posted when boiler goes on. No easy way to access this main vent without cutting insulation or the ceiling so for now will see how this solution works. Appreciate this so much 

ethicalpaul

Consider cutting that insulation and the ceiling anyway. You want to be able to inspect the main vent at will to see if it is leaking or stuck closed.

Alexnyu10

Absolutely will do in the future, would love to have the main pipe replaced for the whole system at some point too.  

Just so I can try to wrap my head around it, what did I change by lowering the PTROL to the bottom/.5 and making sure the inner dial was at 1 (it was about half way off of 1 before I adjusted it). Will this make it so my boiler will automatically shut off when pressure gets too high, or just control the amount of pressure it continuously will maintain the system? 

Thank you again so much for this help 

Alexnyu10

Here is pressure gauge after the system has been running a good bit. So far not hearing that whistle sound. Does this gauge look okay? 

Alexnyu10

bburd

Looks like you have a bad gauge there, or the connection between the gauge and the boiler is clogged and needs cleaning. That is a compound gauge, which measures pressure and vacuum, and should not show vacuum (less than zero pressure) when the burner has been running and steam is up.

The pressuretrol may also be affected by a clogged connection with the boiler and not be operating correctly.

neilc

gotta agree with @ethicalpaul , you want to know, see, and touch, your main vent(s)

Ptrol looks good there,

did you see a high pressure on the gage?
does it always settle back down at -3?
or will that re zero, to 0 ?
does the needle move ?

ethicalpaul

> Just so I can try to wrap my head around it, what did I change by lowering the PTROL to the bottom/.5 and making sure the inner dial was at 1

The pressuretrol's only job is to shut off the boiler if the pressure gets too high and then it lets the boiler come back on when the pressure drops to a certain point (which it will of course do once the fire goes out).

Ideally the boiler won't build hardly any pressure in normal operation, but after it's been running awhile, most boilers will produce steam faster than the radiators can condense the steam, resulting in the pressure going up, which you are seeing.

Your Pressuretrol is known as an "additive" type where the front dial shows the "cut-in" pressure. That's the pressure where the Pressuretrol will allow the boiler to run again after it gets shut off due to pressure.

That front value (.5 now) is *added* to the dial number (1 now) to indicate the nominal "cut-out" pressure. That's the pressure where the Pressuretrol will shut down the boiler if it reaches that 1.5 psi.

But I say "nominal" because this device is notoriously inaccurate and it will probably cut out at more like 2 psi and cut in between .5 and 1 psi.

Alexnyu10

All of these responses are so helpful now I am very seriously thinking my gauge is messed up and I wonder if that is affecting the pressure things ability to shut off. Leaving the boiler off for a few minutes and then I will update to see if the gauge changes at all at that point.

Alexnyu10

Can confirm the gauge is the same whether the boiler is running or off so that’s definitely not working. 

So the heating system itself seems to be working beautifully in terms of getting these 3 radiators nice and evenly hot in 15 min or so, and keeping the house warm, as long as I don’t run the boiler for over 30 minutes continuously I would think the system is working perfectly. And it can easily keep the house warm without having to run that long as long as I keep the thermostat set. 

my plan is going to be to keep the thermostat set at 70 so the boiler never has to run too long, and then hire a new plumber to come by to figure out the gauge and make sure the pressure is right, and also help me figure out the main vent. 

Does this plan sound reasonable and safe an interim strategy? Also reminder this is a brand new boiler and new pipes coming off the boiler replaced as of august 2021, and we just had it tuned up and safety check in September 2022 by plumber that installed it. 

AdmiralYoda

The 30psi gauge is required by code...but is famously inaccurate and almost useless for the typical operating range of steam. If you are feeling handy, for a few dollars you can get some nipples and a Tee and put a low pressure gauge in line with the high pressure gauge. 0-2psi or 0-3 psi would be fine since you are probably maxing out, or at least "should" be maxing out in the 1.5-2.0ish range.

That will allow you to see that actual pressure of the system and still be up to code. I have three gauges lol... the 30psi gauge that never budges and a 0-2psi Magnahelic attached to my Pressuretrol, and a 16oz (1psi) gauge on my Vaporstat. My system cuts in at around 14 ounces of pressure and kicks back on at 4oz of pressure or so.

The Pressuretrol is the backup in the event my Vaporstat bites the dust. Its set for roughly 1.5psi with a 1psi differential.

My system is grossly oversized so I could make alot of pressure if I didn't have adequate controls.

neilc

bburd said:

Looks like you have a bad gauge there, or the connection between the gauge and the boiler is clogged and needs cleaning. That is a compound gauge, which measures pressure and vacuum, and should not show vacuum (less than zero pressure) when the burner has been running and steam is up.

The pressuretrol may also be affected by a clogged connection with the boiler and not be operating correctly.

yeah, either gage is bad, or pigtail and piping there need cleaning,
pull either the gage or Ptrol and literally blow air back into the boiler,
there might be some first resistance as you clear the water in the pigtail, but then you should blow fairly freely,
if not free breathing, then disassemble and snake the pigtail, and or the upper sightglass attachments,
remember to prime the pigtail with a shotglass of water when reassembling,

mattmia2

That gauge may just need to be zeroed with no pressure on it for the elevation at which it is installed. it still isn't precise enough to measure steam system pressures.

ethicalpaul

I don't think the elevation matters (certainly not with that gauge)...the higher or lower pressure due to elevation would push equally on both sides of the gauge, right?

Alexnyu10

And I am at ground level in Flatbush, Brooklyn so I would hope that it wouldn’t be too much elevation.  Also speaking of which, if anyone on here knows a trusted steam heat expert plumber that would be willing to travel to Brooklyn to help me troubleshoot this and repair for a fair price in the next few months please don’t hesitate to let know : ) and happy thanksgiving everyone! Been having so much fun reading articles about steam heating on this wonderful site and grateful this resource exists