Click here to Find a Contractor in your area.
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit

Pressuretrol setting

We have just converted from oil to gas on our one pipe steam system.  The new burner is short cycling, sometimes running for just a few minutes at a time for no apparent reason.  When the thermostat is boosted a couple degrees the boiler cycles in 20 minute intervals before reaching temp.  Radiators are not filling with steam completely even though the furnace has run for hour and the last radiator never gets heat.  The radiators are vented with vari valves and are open, we can here the air escaping but the steam isn't following.  The installers replaced the gortons on the main lines.  The installer came back and said because the house is large (a 2 family with 16 radiators) the pressuretrol needs to be set higher than .5, even though it contradicts everything Dan says, they raised it 1, with no improvement.  I hope someone can help.  We were hoping that replacing our 25 yr old oil burner would provide better comfort and money savings, but so far it hasn't happened.


  • New Problems?

    Did you have these issues with the oil burner, or are these new issues? Was any other work done besides changing the burner?
  • BobCBobC Posts: 4,333
    edited December 2013

    If the thermostat was just installed make sure it is setup for 1 cycle per hour or steam / gravity hot water.

    Varivents can cause problems if they are set to high. It's usually best to vent the mains fast and the radiators slowly to make balancing the system easier.

    As for the pressure, 1-1/2 to 2 PSI is more than enough pressure to heat a 2 family house 95% of the time. Has the boiler been skimmed recently? Is the water in the sight glass moving around a lot while making steam?

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Jamie HallJamie Hall Posts: 6,431
    MDN is right...

    what else was done, besides changing from oil as the heat source to gas?

    Just changing the heat source will make no changes in the behaviour of the system.

    Something else -- or something elses -- was changed.  What?  There are too many possibilities to be able to say "try this, try that" (although there was no reason to change the pressuretrol settings).

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

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • RodRod Posts: 2,067
    Radiator Venting

    Hi-  We need to know more about your system. How many steam mains do you have?

    Do each individual steam main have a Main Vent(s)?  What make and model are they? (you mentioned Gortons) 

     While Vari Valves have their uses, they sometimes cause more problems that they fix. Try this:

     1.  If you have good high capacity main vents, try setting all the Vari Vents on the radiators to their MINIMUM setting.  A Vari Vents minimum setting is about the same as a Gorton #5 radiator vent.

    2.   If you don't have large capacity main vents, try setting just  the vari vent on the last  radiator on each steam main  wide open. (Maximum Setting)  Set all other radiator's vent to the minimum.

     Let us know if 1 or 2  above makes a difference.

    Pressuretrol- Residential  steam systems run at a maiximum pressure of 2 PSI.  If your pressuretrol is subtractive, set the Main to 2 PSI and the Differential to 1 or 1 1/2
  • RreyRrey Posts: 18
    Acting like an underfired boiler.

    Check the rating on the conversion burner. It sounds like alot of the symptoms of an underfired boiler.
  • jp741jp741 Posts: 31

    Thanks for the advice I will check the thermostat was replaced last year to a digital device through the mass save program. 

    So are you saying the pressuretrol can be set as high as 2 in this situation?  I thought I just read the higher the pressure the more you slow down the steam.
  • RodRod Posts: 2,067
    Pressuretrol Settings

    Hi-  "I thought I just read the higher the pressure the more you slow down the steam"

    From a design point this is true and using a Vaporstat with 2 pipe vapor system, you can operate at ounces of pressure. However with a 1 pipe system has its limits and can't operate that low so set the maximum at 2PSI and the differential at 1 or 1 1/2 to start with initially. As you get to know your system better, you might be able to creep it down a bit from there though you'll have to change your control to a Vaporstat as Pressuretrols get very unreliable at lower settings.

    - Rod
  • home owner

    i just converted to gas from oil,the top floor gets very little heat on my steam system. any sugestions
  • home owner

  • home owner

    its a 2 floor house and i own the williamson gsa150
  • jp741jp741 Posts: 31
    electronic low water cut off

    It seems the problem isn't with the pressuretrol or the venting, though they did agree that it isn't building pressure (which they say is okay)....the new boiler comes with an electronic low water cut off and it checks level every 20 mins  shutting down the boiler to do so......funny none of the techs were aware of this.  Now that this mystery is solved, I guess we go about balancing the system. 
  • home owner

    everything was changed, new valves etc
  • MDNLansingMDNLansing Posts: 297
    edited December 2013

    The low water cut off shuts down the boiler every 20 mins to check the water level? Are you sure it's not detecting a low water condition and then triggering a delay before it decides to add water?

    And, BTW, if you're not building any pressure, it's not OK. Your system should be able to build enough pressure to reach the high pressure cut out. This is especially true when it's cold out and the boiler runs for longer cycles. Without pressure, you're boiler runs continuously until the thermostat is satisfied. Ideally, you want it to run up to the cut out pressure, then shut down for a bit and let the radiators give off heat while the pressure falls back to the cut in value.
  • cycleguard

    The cycleguard LWCO works like this.  Shut the flame off for 60 sconds every 20 minutes (I'm not sure what the actual timings are) or so.  The theory of operation is that foaming boilers fool  water level sensors, so shutting the flame off lets the foam settle, and lets the probe get a proper reading.
  • How much is too little?

    The ideal relation of boiler capacity to radiator capacity is for the radiators to be able to condense all the steam produced by the boiler at design temperature (0 degrees in my area).this will cause the pressure to be down to an ounce at full boil, and this well-chosen boiler will never cycle on pressure. The venting has to be capacious. This is all the pressure needed to reach all the radiators in the system, assuming they are correctly (slightly slower-vented).

    This ideal is rarely achieved, but if you only show a maximum of one or two ounces of pressure, count yourself lucky, as no more is needed.--NBC
  • Interesting

    It was my understanding that the Cycle Guard only got triggered when the probed detect a low water condition. It would sense low water, shut down, wait for settle, then decide to fire back up or to call for water from the feeder. I didn't realize it did this all the time no matter what. After reading your post I looked up my notes from a conversation I had with a MsDonnell & Miller engineer and what I stated is what I wrote down. Either he told me that, or my notes are wrong. Either way, thanks for explaining the real function of this thing for me. I was going to use one, but I might need to rethink this. I don't like this idea very much.
  • jp741jp741 Posts: 31

    Attached is the manual from the cycle guard
  • Pressuretrol on Low Water Cut Off

    Just purchased this home.  It has a very old Weil Mclain Gas Fired Steam Boiler Model E-6-B.  Is it normal to have the Pressuretrol mounted to the Low Water Cut off?

    Also my PA404A1033 additive differential does not respond like I expect.  I have the Cut-In set to 0.5 and the Diff set to 1.

    My actual cut-in is 1.5 psi and the Cut-off is 2.5psi....

    any help would be greatly appreciated.
  • oil to gas conversion

    I just had the same problem. Carlin EZ Gas. Orifice was not drilled to proper diameter. Check EDR on radiators and call manufacturer of burner with sq. Ft of steam they should be able to tell you what drill size to use.
  • underfired

    Boiler was underfired, not enough for the connected load
  • FredFred Posts: 5,194
    Pressuretrol setting

    I have a 5000 sq. ft 112 year old home with a 30 year old Burnham boiler (rated at 866 sq.ft. steam radiation) and single pipe steam system. My pressuretrol is set to cut in at .5psi and differential is set at 1 (additive). It has no problem heating all 15 radiators. When the outside temps are below zero, it will, on occassion, shut down on pressure after running for about 45min. to an hour and short cycle, on pressure for one or two additional cycles until the thermostat is satisfied.

    I would think your pressuretrol should be set similarly to mine and work fine.The LWCO cycling every 20 minutes does not seem right or reasonable to me???
  • BobCBobC Posts: 4,333
    If the system

    has a cycle guard on it the boiler will shut down every 10 to 20 minutes of run time depending on which model you have. That LWCO shuts the boiler down to check the water level with a calm water surface and it does so for 90 seconds. The most aggravating thing is it adds up the time and will shut the boiler down when the run time hits the setpoint, if the boiler ran for 19 minutes on the last run, it will shut down after 1 minute on the next call for heat.

    makes no sense at all to me.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • FredFred Posts: 5,194
    Cycle Guard

    Sounds like it should be called a "Cycle Pro" and not a Cycle Guard. That's crazy!
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!