Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Boiler running at 15-20PSI

I purchased my first house 2 months ago and was happy that it was heated by steam convectors. I have heard good things about Steam Heat. It has started to get cold and we have been using the heat pretty much every day. I read the "We Got Steam Heat" by Dan Holohan and he makes it clear that your system should run at 1/2 to 2 PSI. My system is running at 15 PSI regularly and sometimes as high as 20. Obviously not good. So heres some info on my system:

This is a One-Pipe system.
Once the steam leaves the boiler and gets to the header, it splits into 2 Supply Mains, one for the front of the house, one for the back.
Each Supply Main has a main vent at the very end.
Beneath this Main Vent is a 6 inch drip that then ties into the Return.
Both Supply Mains tie into the same Return.

I have an order placed for Pipe Insulation so my pipes will be insulated soon but I figure that does not play a large part in my system pressure. My water seems clean, my convectors appear to be pitched properly, as do the Supply Mains and the Return. The Boiler is definitely a replacement boiler but from what I can tell from the diagrams in the book, it was piped properly.

I have replaced the vents on my Convectors and my main vents.

How do I get the pressure down?

Thank you in advance!


  • ritchie_johnw
    ritchie_johnw Member Posts: 2
    I also realize I could simply have a faulty pressure gauge but when I first bought the house and looked at the gauge it was at 5 PSI so clearly I have a lot of pressure in the system, even if its not quite as high as 15-20.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    That is high!
    Get a replacement gauge, and see if that pressure is indeed true, and then adjust the pressuretrol down as low as it will go. When you have this under control, then get a 0-3 psi gauge, and put it on as well, so you can fine tune the pressure regulation further. The main vents may have been damaged by that pressure, so check them.--NBC
  • icesailor
    icesailor Member Posts: 7,265
    Does the pressure gauge read 5# when the boiler is off? If it does, the gauge is at a minimum, 5# off.

    If the gauge reads 20#, it might mean that the system is operating at 15#.

    IMO, if you don't have the skill sets to immediately resolve this, you really should call a professional. You might have an unhealthy situation.
  • BobC
    BobC Member Posts: 5,471
    i suspect that gauge is bad because if you were really running at 15 or 20 PSI the air vents would first scream and then fail. Also the15 PSI safety on the boiler would have popped off and that would become immediately apparent.

    Check the pigtail to be sure it's not blocked and look at the base of the pressuretrol to be sure the little 1/16" hole at the bottom of the brass fitting is open and not blocked. Then rep[lace the gauge and find out what pressure the boiler is really operating at.

    You mentioned you had two returns tied together, I hope they don't join above the waterline. They should only tie together below the boiler waterline, if they are joined above the waterline all kinds of evil can manifest itself.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Fred
    Fred Member Posts: 8,542
    OMG! This is potentially a serious situation and you need to figure out immediately if that pressure reading is anywhere near accurate or if the gauge is faulty. Personally, I would shut the boiler down and, as Hatterasguy and BobC suggest, clean that pigtail. It has to be plugged up with gunk. How long is that boiler running before the pressure gets to 15PSI? Hours? Does the boiler have a Pressure Relief Valve on it? Does it seem to leak?
  • Fred
    Fred Member Posts: 8,542

    Easy Fred.............it's probably the gauge as well as the pigtail.

    I hope so.
  • wmtandson
    wmtandson Member Posts: 62
    I,ve watched many steam boilers.
    Actually getting to that pressure takes a lot of time
    I suspect your mistaken,but you should get to the reality of it