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Air vent float constantly opens and closes during heat cycle

As soon as the air vents start releasing air, i can hear the float valve constantly open and close until the cycle is over. Bedroom radiator was originally incorrectly pitched which has now been corrected with a level, however the problem continues. Other radiators also mimic this noise but not sure if its as frequent. It was my understanding that these vents will close once there is enough steam and remain closed for the duration of the cycle. The bedroom vent is a watts adjustable air vent. Zero pressure on the system throughout the cycle but i do have two valves that are very slightly leaking.

Is it a matter of steam arriving at the radiator too quickly?

Can a bad vent(s) on another radiator cause this problem of constant opening and closing vents?


  • acwagner
    acwagner Member Posts: 505
    The vents open and close on temperature. On longer cycles, they may cool off some and open back up. The steam will hit them again and they'll close and repeat this process until the call for heat is over.

    Some types of vents make more noise than others when this happens. From my own experience Hoffman 1A vents will make a "click" noise and hiss slightly. I'm not familiar with the watts type, but that may be what you're hearing.

    Is the vent hot when the noise happens? Or is cool to the touch?
    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

  • mrflip99
    mrflip99 Member Posts: 19
    It’s a definitely a metallic click “donk” noise with hissing. Based on what others have said, steam systems can be very quiet and just trying to get to that level. If it didn’t wake me up in the middle of the night I could care less.

    Radiator is warm to the touch, gotta check if it’s the entire radiator or just the top.

    Maybe there is a quieter air vent I can use? Gorton va Hoffman?
  • acwagner
    acwagner Member Posts: 505
    From your description, that sounds like the radiator vent is operating normally.

    The next time it happens see if the vent on the radiator is hot or cold to the touch. If it's hot, then the noise is likely from normal operation. If it's cold, then something else is going on.

    If the noise bothers you, Gorton vents are a good alternative. They have a different mechanism inside that doesn't make noise. I switched to Gortons for that reason.
    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

  • mrflip99
    mrflip99 Member Posts: 19
    @acwagner is this the noise you were expecting to be normal? Also, sounds like a good amount of pressure right? Check your volume before playing, kind of loud:

  • mikeg2015
    mikeg2015 Member Posts: 1,180
    Might have some boiler surging. That will rattle vents.

    Adding more main venting might reduce system pressure and slow down steam movement to the radaiator vents.

    Also, sometimes if radiator vents are too fast, steam races across the top and mixes with air and you get more noise.
  • gfrbrookline
    gfrbrookline Member Posts: 639
    The watts vents are what HD used to sell, not very good quality.

    Replace them with a good quality vent like Ventrite No.1, they are virtually silent if your pressure is set correctly. Check your boiler pressure, your pressuretrol may be set too high. It should be set to cut out at no more than 1.5 psi, less than 1 psi is optimal.
  • mrflip99
    mrflip99 Member Posts: 19
    @mikeg2015 I haven’t sat and watched the boiler during a full cycle yet, but the last time I sat and watched til the main vents closed, no surging in sight glass. Currently have a Barnes and jones big mouth vent on there at the end of dry return but need to add antler since it’s at a T. You think that’s enough?

    @gfrbrookline will def check out vent rites. I installed a 0-3 gauge and barely saw the needle go up during these cycles, but again haven’t watched an entire cycle yet. Pressuretrol was verified/calibrated by a steam pro so I think that’s good.

    Few other facts about my one pipe system:
    - oversized boiler at 325 edr when I only need 222 edr
    - there was a history of high water usage and gas ( May have been corrected by a full boiler clean and corrected gas WC increase)
    - I have 3 of 7 valve stems with a slow drip during cycles, maybe that’s why there is no pressure building? (Will be replaced in the upcoming week)
  • acwagner
    acwagner Member Posts: 505
    @mrflip99 that sounds like the vent operating normally. You're building pressure when all or most of the radiator vents close. The trick is to avoid that if you can.

    A few questions:

    - Does this happen on a regular call for heat or when recovering from a temperature setback?
    - Do your radiators start heating up at roughly the same time, or do they heat up in sequence from first on the line to the next with several minutes inbetween?
    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

  • mrflip99
    mrflip99 Member Posts: 19
    edited October 2019
    @acwagner How do I prevent the building of pressure when most radiator vents close? Heat the main evenly first before allowing steam to rise in the risers?

    - Occurs at regular call for heat.
    - I have a feeling that the radiators heat in sequence but will have to confirm. I usually hear one radiator begin to vent and then another. (I have two mains from the boiler one that goes to the right and one that goes to the left. The right tends to make clicking/hissing noises first then the left main radiators which are closest to the thermostat)

    If it’s in sequence, is this why I hear the constant clicking — its filling one riser at a time and when it goes on to the next it pulls some of the steam from the first causing the vent float to drop before refilling again? do I need to allow more main venting so the radiators heat up at the same time?
  • Jamie Hall
    Jamie Hall Member Posts: 16,100
    On preventing the pressure rise when the vents close.

    Two steps. First, make sure that your main venting really is adequate. You can and probably should get a low pressure gauge if you don't have one -- 0 to 3 psi -- and put it on the boiler. What you should see as the boiler fires is the pressure rise to perhaps 4 OUNCES and then level off until the radiators are mostly filled. If it goes much higher than that you may need more main venting.

    Second step. Set your pressuretrol (since you don't have a vapourstat, I think?) to cut out at as low a pressure as you can (be careful not to go too low -- they fall apart if you try to set them too low). Certainly not more than 1.5 psi. Differential can be 1 psi.

    With a boiler that oversized, the system is going to cycle on pressure. No way around it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • acwagner
    acwagner Member Posts: 505
    First step will be trying to balance your radiators. Then deal with the oversized boiler. If your radiators are not balanced, then the first radiator will fill up first and start making noises before the others even get steam. If they are balanced, then it's possible all the radiators will only get partially filled before the thermostat is satisfied. Then the vents won't see any steam and won't make noise, and you won't be building up pressure. That may not be possible with your system, but balancing it is am must either way.

    This PDF gives a good approach to balancing a single pipe system, and also lists the venting capacity of radiator and main vents.

    Focus on getting your two mains balanced. Next time the boiler turns on (or force it on yourself) use a timer to see how long it takes steam to get to the end so of each main. You want them to the same if you can, or pretty close. You may need to add vents to one or the other.

    Use the same approach for your radiators to see how far off they are from each other.

    If they are way off, you'll need to start adjusting the radiator vents. This will take some trial and error.

    As @gfrbrookline said, the ventrite are a good vent to use because they are adjustable. I'd never used them, but others like them. I'm more partial to Gortons, but venting on Gortons is fixed. So if you need more or less venting you need swap it with a larger/smaller gorton vent. Can get pricey if it takes a lot of adjustments.
    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

  • dopey27177
    dopey27177 Member Posts: 624
    Because you stated the boiler is grossly over sized you should have your oil suppliers install a smaller nozzle in the oil burner or if gas fired have the gas company turn down your firing rate.

    This will prevent your boiler from short cycling.

    Once that is done you need to have a drop back pressure to allow the vent valves to cycle properly.

    Typically the drop back should be 1 1/2 Psi.

    Using all different types of vent valves may case a slight problem.

    As to installing more main vents you do not buy efficiency, you waste time and money.

    Remember steam is flowing at anywhere from 30 to 45 miles per hour in your system so the delivery of steam is pretty quick, the only problem is getting air out of the system.

    A grossly over sized main vent will not make much of a difference in venting the steam main.

    A Gorton D vent will vent 4 cubic feet of air per minute at 1PSI
    A Gorton # 1 vents the same amount of air per minute.

    Remember your boiler will begin to supply steam at start up in about 10 to 20 minutes,

    While steam is flowing before the system pressurizes air is being vented from all the air vents int the system.

    How much air is in the system.

    Measure the internal cubic feet of space in dry side of the boiler.

    Measure all the air space in the piping system and radiators and you will see there really is not much air in your small heating system.

    Jacob Myron

  • Chris_L
    Chris_L Member Posts: 206
    @mrflip99 Do you know what kind of vent you have on that radiator? (I couldn't see that information in the thread).

    Can you post a picture of it?

    I am guessing from the sound it is a Ventrite No.1. I monitor my tenant's steam pressure and will hear the same sound when their living room radiator Ventrite 1 closes at 8 oz. (I only hear it once because my system shuts down the boiler for a few minutes after that.)

    As other have said, keep the pressure low. But don't expect it to eliminate that noise. You've got a noisy vent.
  • mikeg2015
    mikeg2015 Member Posts: 1,180
    What vent do you have? It’s counterintuitive, but you often need slower vents, and more main venting to control the steam better. vent too fast and steam doesn’t fully fill the radiator heat the sections fully, which actually reduces radiator capacity and makes the boiler even more oversized in comparison.

    If the radiators are not heating up evenly, then you need more main venting.... and possibly slower vents. It’s the ratio that matters as much as anything... until you start building pressure.

    Honestly, I’m finding that most vents out there are too fast. A Groton 4 & 5, Hoffman 40 splits the difference, and ventrite is adjustable and covers the full range.
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