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System over pressurizing all 9 radiators

Really frustrating situation here. All 9 of my radiators begin expelling steam at .5 psi and are simply screaming by the time the pressuretrol cuts out at 2.25.

Changed all radiator vents this season. Since doing so, all radiators began displaying the symptoms above. I couldn't get any readings on my old 30psi gauge so then the work began:

changed the pigtail which was 100% clogged and refilled it with water.

Swapped the 30 psi gauge to a 0-3psi

changed the pressuretrol, replaced with same model.

Changed main vent from old 1/4" (likely clogged) and built a 3/4" riser with T at the top leading to TWO 3/4" main vents. The only main vent in the system is on the return, just above the equalizer and unfortunately right at the 90' - which is why I put a 6 inch riser on that.

Boiler fires and pressuretrol kicks off at 2 psi and kicks back on at .5 psi as expected which takes a full 50 minutes of firing to achieve.

However, the steam has all the radiators hot within 12-15 minutes from cold start - not bad at all! It then continues to fire until the pressure reaches .5psi (this takes about 40 minutes) At that time, all 9 radiators are pushing steam out of their vents. By the time the pressure reaches 1.5psi, each vent is shooting steam out so hard that the paint is being flicked off the radiators. Once it reaches this psi, all 9 radiator vents are rattling like baby toys. The pressuretrol kicks off at 2psi and the living conditions in the house are intolerable due to the insanely loud hissing.

I replaced all 9 radiator vents again. No luck, same symptoms.

Any thoughts??


  • Dan_NJDan_NJ Member Posts: 118
    Clearly something is not right. I can't imagine all 9 vents are bad twice in row. My first impression is that the pressure reading is not accurate and exceeding by some amount. How confident are you in your 3 psi gauge? What type of vents have you used so far and where did you get them? And do you have any of the original vents (any that were not spewing originally) and if so can you put one back in service and see if it behaves the same way?
  • Jamie HallJamie Hall Member Posts: 13,118
    Whoa. Let's step back here a moment. First observations: All the radiators are hot in 15 to 20 minutes. Pressure then rises to 0.5 psi at about 40 minutes. Radiator vents are still open at that point

    The radiator vents should be closed when the radiator is hot. I agree that it is a bit odd that all nine vents should be bad -- but if the pressure reading is off, they might be being overstressed. One way to check would be to get one really good known high quality vent (I prefer Gorton or Hoffman) and stick it on and see if it does the same thing.

    That said, there is no point in running the boiler beyond where the radiators are hot. You are talking about perhaps as much as 20 minutes of running time you don't need. Since a pressuretrol cannot go reliably to less than 0.5 psi cutin/1.5 cutout, you may need a vapourstat -- but lets' think about that later.

    But a critical question: when you took the pigtail off, did you also check to be sure that the tapping into the boiler was free and clear? Does the pigtail go directly into the boiler, or is it on the low water cutoff? In either case, the opening into the boiler must also be free. This is particularly true since you say that you put your 0 to 3 psi gauge in place of the 0 to 30 gauge (don't tell your insurance company; the 0 to 30 psi gauge is required by code; the 0 to 3 psi gauge should be in addition to the 0 to 30). Therefore the 0 to 3 gauge is not necessarily reading the same pressure as the pressuretrol. The best way to mount the 0 to 3 is to connect it -- with a T and a few fittings -- to the same pigtail as the pressuretrol. So I'd fix that.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Hap_HazzardHap_Hazzard Member Posts: 2,263
    What kind of radiator vents are you using? If you're not sure, post some pictures.
    You can test the vents by blowing into the connector fitting. If you turn the vent upside-down, no air should escape. (This doesn't necessarily mean it's good, but it does mean the valve works.)
    Just another DIYer | King of Prussia, PA

    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • MikeBBudlongMikeBBudlong Member Posts: 8
    @Jamie Hall

    The radiator vents all stay open as expected, and then close as soon as steam reaches them, as expected. They stay dead silent and perfect until the pressure hits about .5 on the gauge, at which time, ALL radiators begin to hiss in unison. I fear there's so much pressure that it's entirely overwhelming the mechanisms.

    I had already checked the block and tapping and it's clean and clear. I attached a 4" to 90 to the block and then put the new straight pigtail on the 90. T'd off the pigtail, 2" nipples on either side, street 90 to Pressuretrol on one side, 90 to 0-3 gauge on the other. Is the 4" and 90 off the block messing with the pressure? Now that I think about it, there's going to be air in that 4", would that be able to escape and would it affect the function of the downstream pigtail/gauge/ptrol? Should I put the pigtail directly into the block?

    I feel the gauge is accurate because the ptrol is cutting in and out exactly where it's supposed to. Unless the brand new ptrol is also lying....

    I have taken the pigtail (with t, ptrol, and gauge attached) off of the boiler and can blow into it and see the gauge jump as expected. Nice and easy... My gut feeling here is that the entire ptrol/gauge setup is not receiving an accurate reading from inside the block. The oddest thing is, this is behaving EXACTLY like it had when the fully clogged pigtail was on it a few days ago.
    I swap literally everything out and all the same symptoms remain lol.
  • gerry gillgerry gill Member Posts: 2,985
    Sounds like boiler may be to big. Or firing rate needs to be lowered.

    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • FredFred Member Posts: 8,423
    What LWCO do you have on that boiler? If it is a Cyclegard, the boiler may be shutting down every 10 minutes to check water level and you are assuming the Pressuretrol is shutting the boiler down on pressure. Clearly, either the pressure is well above 2.5 PSI or none of those vents are closing when steam hits them.
    It also seems unusual that your boiler is running for 50 minutes a cycle, especially if the rads are hot in 10 to 15 minutes. You do realize that the Pressuretrol is only set at.5 to allow the boiler to re-fire on the next heating call and the 2 PSI Cut-out is to ensure pressure never gets out of control. You should not be testing how long it takes to cause the Pressuretol to shut the boiler down by turning the thermostat way up to extend the heating cycle. Under normal circumstances, the Pressuretrol should not shut down the burner on a typical heating cycle, the thermostat should do that. I'm not sure if this is a mechanical problem or if you misunderstand how the Pressuretrol is suppose to function. I feel like you may be making the boiler run for extended periods, well beyond what is necessary to satisfy the thermostat at a normal, comfortable temp???
  • MikeBBudlongMikeBBudlong Member Posts: 8
    @gerry gill

    Possibly, but this all functioned perfectly for the first two seasons, and, if it were too big and making too much steam/pressure, I would expect the gauge/ptrol to step in and cut it off.

    The radiators are steaming soo much that when the ptrol finally does cut the fire off, the gauge drops and it refires within 30 seconds.
  • MikeBBudlongMikeBBudlong Member Posts: 8

    I did this to all 18. When upside down, no air, if I rotate it to upright with pressure still on, it opens as expected due to insufficient heat from my breath. They all appear to be working just fine.
  • Jamie HallJamie Hall Member Posts: 13,118
    Ah. One more useful bit of information. You say that the vents close on steam, as they should, and then later -- as the pressure rises -- they start to hiss and generally misbehave.

    Something is clearly amiss with your pressure readings. Ther boiler should shut off on pressure long before the vents staMany vents will start to misbehave at around 3 psi; virtually all of them will at around 7. Somehow -- maybe the pressuretrol (the way you've piped it sounds OK), maybe the gauge, maybe... ??? I'm not there to look! But something is quite wrong in terms of pressure.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • SuperJSuperJ Member Posts: 579
    Are the gauges and pressuretrol off the same pigtail? Perhaps they agree because they're reading off the same restricted source?
  • Hap_HazzardHap_Hazzard Member Posts: 2,263
    Those look like USAV 880B vents. Not the greatest vents, but probably not the root cause, and the fact that they're all behaving the same indicates that they're consistent if nothing else. I think the max operating pressure is 5 psi, so maybe those nine vents are saying your pressure gauge is wrong, but the p-trol should open the circuit long before the pressure hits 5 psi.
    Just another DIYer | King of Prussia, PA

    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • Mike CascioMike Cascio Member Posts: 140
    Those vents are JUNK. Get some gortons, hoffmans, ventrites even Maid O Most before these Home Depot vents. Try replacing one vent with a hoffman 40, ventrite 1, or a gorton/MOM #5 and see what you get.
  • Hap_HazzardHap_Hazzard Member Posts: 2,263
    edited November 2019
    I don't think replacing one vent would shed any light on the problem. Suppose he installs a new vent with an operating pressure of 10 psi. When the pressure hits 5 psi, the other eight vents start leaking, but the new vent holds, so it looks like the new vent is better and he goes out an buys eight more and installs them. Now the pressure goes up to 10 and all the vents start leaking again. I'm not sure he would have gained anything by spending all that money on vents. Even if his pressuretrol finally cuts out at, say, 7 psi, before any of those new vents start to leak, he still hasn't fixed the problem. While the symptom may have gone away, he's still running with way to much pressure in his system.
    Ultimately I think he's going to need to spend some money on vents, because it's pretty unlikely that you can achieve anything like good balance by installing the same vents on all your radiators, but there's something wrong with the pressure control that needs to be addressed first.
    Just another DIYer | King of Prussia, PA

    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • acwagneracwagner Member Posts: 414
    My personal experience is that vents will make noises when you get above .5 psi, and definitely when you're over 2psi. It's just best to avoid building pressure to that level. I bet your controls are all OK.

    Is this happening on recovery from setback or a typical call for heat?

    Is your system balanced? Or do the radiators heat up in sequence one after another? 50-ish minutes of continuous heat seems like a long time to satisfy the thermostat set at constant temperature.

    What kind of thermostat do you have?
    Burnham IN5PVNI Boiler, Single Pipe with 290 EDR
    18 Ounce per Square Inch Gauge
    Time Delay Relay in Series with Thermostat
    Operating Pressure 0.3-0.5 Ounce per Square Inch

  • FizzFizz Member Posts: 522
    I recently experienced same issue on single pipe system, and I was the source of problem. My radiator in thermostat room had MOM-D vent but was experiencing over-shooting in room, though my pressure reading was between 2-3oz when t-stat would shut-off, so I switched-out D with 6, result was longer run-time, no overshoot, but pressure build-up to 16-20oz causing hissing of all vents(8) and pressuretrol shutting-down system. Replaced 6 with C and everyting is ok, no overshoot, pressure 2-3 oz, t-stat shutting-it down.
  • MikeBBudlongMikeBBudlong Member Posts: 8
    Ok folks, I've got this solved!

    I ended up purchasing 3 new vents of different types/brands to try them. All 3 were better, and one (Maid-o-Mist) did not make any unwanted noise (other than normal stuff).

    Back to the store. Replaced all vents with Maid-O-Mist with the correct number based on their location in the house. Fired up the boiler and it was perfect. All heat came up at the same time (12-15 minutes from cold start), all vents shut, pressure built twice as fast as before, reaching 2.25 psi in 30 minutes instead of 55, and NO hissing even at the 2.25 psi cut-off. I allowed it to cycle through several more times by keeping the thermostat higher so I could test the ptrol. Out at 2.25, in at .5 like clockwork. 5:45 seconds of burn, 3:30 seconds off while pressure dropped. Now I can raise the temp in my house more than one degree at a time if I wish - imagine that.

    The system has never behaved so well in the 3 seasons we've been here. It's nearly totally silent now.

    I cannot believe that I bought two complete sets of bad vents from two different vendors lol. The chances seem slim but it happened....

    Getting to know this system so well in the past few weeks has made me realize that the entire system heats completely WELL before the pressure on the gauge even begins to move - which makes me think that I should explore adding a good VaporStat in series with the ptrol to dial in even more efficiency. Is this possible/recommended?
  • Hap_HazzardHap_Hazzard Member Posts: 2,263
    The main adantage of the vaporstat is that it allows you to accurately set your pressure in the 0–24 oz range, but if you're already operating in that range without cycling on pressure, it isn't necessary.
    Just another DIYer | King of Prussia, PA

    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • MikeBBudlongMikeBBudlong Member Posts: 8
    Thank you all for your help, and for the wealth of knowledge on this site in general. I knew nothing of steam until I bought this house. I am pretty hooked. They're fascinating.
  • ethicalpaulethicalpaul Member Posts: 1,665
    edited December 2019
    See if you can get the cutoff down to about 1.5

    And congrats!
    1 pipe Utica 112 in Cedar Grove, NJ, coal > oil > NG
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