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steam not making it to top floors

Summit_heatcool Member Posts: 10
edited November 2021 in Strictly Steam
1 pipe steam with recently replaced heat timer EPU-D.

hest timer set point F

it’s running on .6 psi and reaching its vapor stat set point very quickly.

it then shuts off and quickly the vaporstat calls again and boiler turns on. this keeps repeating.

eventually the steam gets to the top floor but does not stay for long enough to heat the top floors.

should i change the heat timer settings?

should i try to find air vents and verify sizing and operation?


  • Jamie Hall
    Jamie Hall Member Posts: 23,313
    If it's reaching a pressure of 0.6 psi very quickly, your venting is inadequate. But not the radiators -- the main venting. You may need riser vents as well.

    That said, the vapourstat cutout of 0.6 psi is probably too low. Most one pipe systems seem to be happiest somewhere around 1 psi. Not that they get there until the main vents close, but after they close they need the slight additional pressure to get the steam to the radiators (Note: SLIGHT additional pressure!).

    If the steam is getting to the top floors bur the heat timer shuts off the boiler before you get much heat up there... well, first fix the venting, then check again. But if the problem continues, which I suspect it will, um... yeah... maybe the heat timer needs to let the system run a little longer? Since the heat timer is just that -- a timer -- and is really stupid about how long it takes steam to get to where it's needed. You have to tell it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 15,533

    I don't know that heat timer model but most all steam heat timer controls have a "steam established" sensor. Typically this sensor is placed at the farthest point in the system and keeps the boiler running when the sensor senses steam the control starts timing and will keep the boiler running depending on the outdoor air temp. It will shut down and restart on pressure while timing if the pressure gets too high.

    Bottom line, fix the venting as @Jamie Hall mentioned make sure the heat established sensor is in place and working then tweak the controls adjustment as needed
  • Summit_heatcool
    Summit_heatcool Member Posts: 10
    thank you for all this information. Very much appreciated.
  • dopey27177
    dopey27177 Member Posts: 887
    Thhe sensor for the Heat Timer must be at the farthest end of the system. Usually on the return pipe. In your case with a one pipe system it should be placed at the end of the dry return. Set the temperature of the sensor at about 190 degrees. Close to steam temperature. Additionally, set the vaporstat at about 1.5 psi off and 1 psi on.

  • nicholas bonham-carter
    Actually, a HoneyWell VisionPro thermostat, with its remote sensor on the top floor would do a better job than the Heatimer.
    check that your main venting enables only 2 ounces of back pressure on your low pressure 0-3 psi gauge.—NBC 
  • Summit_heatcool
    Summit_heatcool Member Posts: 10
    Boiler starts and makes steam and the vaporstat with in 4 min is satisfied. about 30 seconds later it closes again and asks for steam. The vapor stat is on and off multiple times during heating cycle. 

    I’m attempting to get to the main vents as i’m suspecting this is the issue with the boiler vaporstat satisfying so quickly.

    the building is a 6th floor apartment building in boston.

    the 5th and 6th floor are not getting heat with the short cycle times.

  • nicholas bonham-carter
    Is there any anticipation in the heatimer, to prevent temperature overshoot?
    many people have had problems with them as they were sold to cure venting problems, which of course they could not do.
    The salesmen were happy no doubt, sitting in their sailboats in the Carribean, next to the boiler chemical reps!—NBC