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4 pros stuck! The mystery of the gurgling radiators

As the title says, all of last year i had issues with my radiators. The vents would always hiss and gurgle and spit drops of water towards the end of the heating cycle. The pig tail has been replaced. The honeywell pressurerol is set at 1 main and .5 diff. I've lived here for 32 years. Same boiler, same rads, there has been no repairs since it was installed 40 years ago. The system has never had main vents so the pros who came out ruled that out. No one can figure out why the vents are quiet during the whole cycle and then they start hissing at the very end! ☹️

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 19,424
    Somewhere condensate is slowly building up and finally gets deep enough to be carried into the radiators. There could be lots of reasons for that, but I'd start by looking for very slow wet returns or slightly off pitch "horizontal" mains.

    Do you also see a very slow drop in water level in the boiler during a long steaming run?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • massarottob11
    massarottob11 Member Posts: 3
    Somewhere condensate is slowly building up and finally gets deep enough to be carried into the radiators. There could be lots of reasons for that, but I'd start by looking for very slow wet returns or slightly off pitch "horizontal" mains. Do you also see a very slow drop in water level in the boiler during a long steaming run?

    Normally, i would see a drop in water and then after about 30 minutes the water returns and the sight glass returns  back to the same level it was before the boiler started. It's possible the wet returns could be the issue. As i mentioned the rads are quiet until the very end, just before the boiler shuts off

  • Jamie Hall
    Jamie Hall Member Posts: 19,424
    30 minutes after the boiler shuts off? Too long. Look for partly clogged wet returns.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • massarottob11
    massarottob11 Member Posts: 3
    30 minutes after the boiler shuts off? Too long. Look for partly clogged wet returns.

    How can i clean them/flush them? never done it

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,633
    edited September 23
    Your discussion title sounds like an Agatha Christie novel. Or perhaps… a case for Sherlock Holmes. Since it has not been done in 40+ years, you may be looking at cutting pipes open. If there are unions at strategic locations, that may be a good place to start. You may even have some valves  available to open but they may be unable to open and close after all that time.  .

    Regular maintenance would have exercised those valves (if there are any valves) and plugs or caps that are removed from time to time will make flushing out sludge much easier. 40+ years can make separating those fittings near impossible 

    But consider this.  If you paid for a good flush every three to five years over the last 30 years, you may have spent more than this major piping job will cost (adjusting for inflation)
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org

  • clammy
    clammy Member Posts: 2,766
    Maybe they are not hissing but sucking ,I ve seen this occur after the boiler cycles off the system pulls a vacuume and the vents hiss ,if you had a low pressure gauge you would be sure the boiler is not producing pressure and w a vacuume gauge it may show the system going into it as it cools down . I ve run across it once in 40 years and they where recessed sunrads w no insulation behind them . Have also witness kinda the same but on a 2 pipe but the noises where durning the cycle .peace and good luck and as Ed has said maintance is key clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • ChrisJ
    ChrisJ Member Posts: 13,258
    What condition is the boiler water in?
    Is it oily or dirty looking in the gauge glass?

    Just because the Pressuretrol is set somewhere doesn't mean it's actually working correctly.

    Just because the system never had main vents doesn't mean it doesn't need them. Obviously this is a separate subject, but you need them.

    The only time I've had radiator vents hiss at the end is when most of the radiators are near full of steam so the system pulls a good vacuum when the boiler shuts down. So, I'm going to guess for some reason your thermostat is calling for heat for a long time. No idea why, but I'd expect the house to be very hot when the system finally shuts down.


    Please supply pictures of the boiler, all of it's piping, the gauge glass, some or all of the radiators and their vents and the thermostat.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    dabrakeman
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 999
    2 other things to look at besides clogged returns...Very dirty boiler water and possibly a large boiler or system leak. A leak will bring in lots of fresh water and the pollutants stay in the boiler as the water boils to make distilled water in the form of steam. Those pollutants build up over time and can cause the boiler to not boiler properly, getting water up into the system. Is the boiler overfilled?
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