Loud hissing from nearly all radiators during this cold spell

It could be that the main venting is not functioning or improperly sized.

What pressure is the boiler operating at during a long cycle?

has someone ben servicing the pigtail on the boiler that goes to the pressuretrol?

btw there are less pretty but just as effective TRVs for single pipe radiator vents from a number of other manufacturers. Remember the TRV can only stop a 1 pipe radiator from heating at the begining of the cycle, once it is already heating it can't stop the heat so your boiler needs to cycle somewhat frequently and you need to have the system more or less balanced to begin with for them to work well.

I guess i would need to know what the noise is. Steam flowing makes a little bit of noise, the air vents can make some noise, the vents can make more noise if the main vents aren't working. is it @JohnNY 's toro plumbing? They should be able to sort it out for you or tell you if it is normal. John is one of the best residential steam people. You could end up with more pressure on a couple remaining vents if the mains and most of the radiators are full of steam or if a TRV opens on a cold radiator while most of the system is already filled with steam.

If you are trying to use the TRVs as individual thermostats for each room rather than to tame a few rooms that are overheating, if many of them are closed then the air is going to make more noise getting out of the few remaining radiators.

if a bunch of the radiators aren't heating then the air that should be venting out of those radiators is all going to be trying to vent out of the few radiators that are heating and it will be noisier. figure out why the other radiators aren't heating. was it skimmed a few times after it was installed and after piping was changed? if it is surging you will likely have problems with part of the system not heating.

It's normal. Steam is FAR from silent on cold days like we have right now (even with proper main venting, working radiator vents, insulation on the pipes and pressuretroll set to less than 2 psi.)

Side note 1. Learn a bit about your boiler and your vents or you gonna chase an endless loop of ineptitude (and still pay $$) or have an expert fix it for $$$.

Side note 2. This site is a great resource so you are not that far away from becoming an expert yourself.

Listen to your system and it will tell you what is wrong with it. My single pipe system started to tell me something was wrong about a month and a half into this heating season. I knew that I should have drained and flushed the boiler and the returns but I was a bit beaten up from the 16 ft steam main replacement job I did myself and skipped it. It sounded nice and silent at the beginning of the season with just a whisper of sound coming from the vents and very little panting. Then the panting got worse and started to hear startup bang when the wet steam hit the end of my steam main. Going down into the basement revealed the surging in the sight glass and I knew what was happening.

Now, after draining and flushing, even at 3deg F yesterday everything was back to being nearly silent.

I think you have had some people doing work, and for a jacked up price, that have done less than right by you. One of the classic things they will do is crank up the pressuretrol setting rather than try to find out why the system isn't balanced, and that's an easy thing they can do and get themselves out the door. Again, you really should take a picture of your pressuretrol with the cover on and off and we can see if this was done. If lowering the pressure setting doesn't allow even heating to all the radiators, then you need to proceed from there.

Also, a few pictures of your near boiler piping, from different angles. You'll really get a lot better help here if you do these things on your end.

I can add in as others have………when running properly, the system should be pretty quiet. I have a single pipe system (in northern NJ, not that it matters where it is) and these past few days with it getting down to 0 degrees F it's been just ever so slightly noticeable in extra venting noise. But I'm just tuned it to what my system sounds like when it's running at 20 degrees vs 0 degrees. I will add in………a few weeks back my pressuretrol was sticking, the system was getting up to 1 psi until it shut off. The amount of vent noise the system made when at 1 psi was significantly more than when running at very low (normal) pressure. My low pressure gauge is a 0-5 psi, and the needle sits on the 0 stop when the system is running normally.

Those few weeks back at 1 psi (with a sticking PT) even my wife was asking about all the radiator vent noise was about………the experts here on this site will guide you in the proper direction, just get them the pictures of your system that they ask for.

What kind of Pressuretrol do you have that you can set the cutout to as low as 1psi? Mine is Honeywell (additive) and lowest setting is 1.5 psi cutout and 0.5 psi cut-in. It sounds suspiciously like your pigtail is clogged and you might be getting much higher than 1 psi and don't know it. If you haven't done so recently, I'd clean that pigtail.

My boiler is way oversized so it cycles on pressure. The colder it is, the more it cycles and spends more time at the high pressure limit. Things I've learned over the years:

1. I had no main vents. The radiator vents then have to bleed all of the air in the system before the steam can actually get to the radiators. I installed some main vents and now the only air that needs to escape the radiators is the air that is actually in them.
2. Before I knew better, my pressure was set too high at 3psi. I've since turned it down to 1psi after installing a vaporstat. Even without main vents that made a big difference.

Before these adjustments my radiator vents would bang open…followed by a long, loud hiss….then slam shut. Multiple times each heat cycle. I thought it was normal, it isn't.

If a boiler is properly sized for the EDR of the radiators and the mains are properly vented, the operating pressure even on the coldest day will be ounces, not pounds of pressure. It will be completely silent.

As others said, lets see some pictures of the boiler controls so we can see what pressure you are operating at. And some pictures of your main vents also if you have any.

You should only hear a slight and brief whistle as the vents close and pressure starts to build. No system is perfectly balanced and the last vent to close in the house may make a tad bit more whistle. But it should last for a very short time and then go silent. If there is prolonged whistling/hissing, then something is wrong with that vent and/or the pressure in the boiler is way too high.

@ Captain Who - pigtail is brand new from this past November and I rechecked it a month ago to make sure it wasn't clogged. It was as clean inside as the day I installed it in November.

AFA as the PTrol, it's a Honeywell set just above the 0.5 mark cut in mark. My 0-5 gauge (also brand new) it teed in just below the Ptrol above the pigtail.

All I know is that the system runs silent, provides plenty of heat, and reads 0 on the 0-5 gauge all the time……….except for that one time the system was running continuously and reading 1 psi (maybe slightly above that). The knowledgeable personnel here mentioned that it may have a stuck Ptrol and would not shut off the system properly. I ended shutting down my thermostat, manually activating the Ptrol switch a few times and lubricating the pivot joints with some light lubricant. Seems to have taken care of it as the issue has not returned. Plan is to put in a vaporstat, I was actually going to send out a message asking what the correct one to use was. But that's for a different discussion………..lets's help the OP with his steam system issues in this discussion.

@Goodhap I am experiencing the same issue of long sustained hissing on some of my radiators. I replaced a broken main vent that was probably 50+ years old, added another main vent in an attempt to 'balance' my single pipe system, and sized the correct radiator vents for each of my radiators based on my calculations. The system was dead quiet at the beginning of the season but as it got colder there are periodic instances of loud hissing. I think we may be in a similar situation.

I have completely replaced my pigtail and confirmed that my pressuretrol cutout is <2 psi. I think my old honeywell presseretrol is not functioning correctly because it never goes to pressure cut off as the system cycles naturally. I think the issues lies with the overall pressure of your/my system in that the presseuretrol is not working, thus the PSI in the system is too high and not being regulated safely/efficiently.

You would know what is happening if you put a 0 to 3 psi low pressure gauge in. Then, if the pressuretrol is malfunctioning it would be immediately apparent and you wouldn't be wondering.

@ChrisJ thank you. I still get hung up that it never hits the cut off limit. Ever. I know that these units can be a bit temperamental and I have tried to use a screw driver to adjust the spring, but it never really seems to work. I've sat there while the system ran and it will run nonstop until the periodic low water test stops the boiler.

@Captain Who thank you. I have thought of this but was not able to get around to it last season. I feel like I read a thread here where someone suggested that but they commented something along the lines of (sic) "The pressure gauge never moves when the boiler is operating". Don't hold a gun to my head on this line of thinking but I feel like that made me skip adding a pressure gauge in line with my pigtail and pressuretrol.

Try to clock the meter or have someone measure the gas pressure. Boiler might be over fired

And always confirm that the pressuretrol is functional. It isn't just for efficiency. It is also 1st line safety feature before the Pressure Relief Valve.

Another issue is we have to establish the difference between normal venting of air and faulty venting of steam. People say "hissing" but different people use different words for what they are hearing. If the vents are leaking steam, as shown by placing a dental or inspection mirror at the outlet and looking for fogging or water droplets, then they are either defective or the pressure in the boiler is above their ability to stay closed.

So check them for steam leakage first. Then find out what the pressure in the boiler is with a gauge and then check to see if the pressuretrol is functional on a long heating cycle from a setback or something.

@Day_Tripper, you are playing with the wrong screws. They key is in the back of the pressuretrol.

(Silent Steam Team has many great videos, plus mine i've linked to above shows how to fix it too)

I know I watched a few of Silent Steam Team videos on this. Go through these ones:

https://www.youtube.com/@gordonschweizer5154 /search?query=pressuretrol