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TP Valve on a Steam Heat System

benraymond | Posted in Energy, Heating & Insulation on October 9, 2002 08:47am

Hello everyone,

I have an old steam heat system (looks to be at least fifty years old, gas-fired, a one pipe system). It’s the type you have to turn a valve to fill with water every once in a while. Lately the Pressure release has been blowing off regularly on the top of the boiler, filling my basement with steam (maybe I should take up steam bending).

We had a plumber over on a separate job a while back (new bathroom). He looked at it, scratched his head, promised to take care of it, and then disappeared when the job was done. Not filling it as high does help somewhat, but I used to fill it that high before.

Do these valves just fail with time? Is there something that increased the pressure in the system? Can I just wrench the thing off and go to my local plumbing supply and buy another valve? Are there standard valves I can use? Is there any chance I’m going to blow up my boiler if I get the wrong pressure relief type?

Any replies greatly appreciated,

Ben

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  1. brucepirger | Oct 09, 2002 09:11pm | #1

    Ben, I'm no expert, and soon you'll hear from some here...

    BUT DON'T IGNORE THIS OR BOLT THE VALVE SHUT!

    Yes, you could have serious boiler explosion issues.

    We have all heard the story of some dumb a$$ (often landlord) who just caps off the TP valve...only to send the boiler or water heater through the roof, wall, floor, whatever...often killing in the process.

    Don't ignore this one...

    1. NormKerr | Oct 10, 2002 12:47am | #2

      the pressure valve on your boiler is one of the most important safety features on your system.

      Fix this immediately.

      Find a STEAM EXPERT in your area (they can be rare and do NOT just accept some plumber's word that "he knows what he's doing", because steam heat is a very old science that is not currently taught in any of the main-stream plumbing or heating schools. Ask around, get references from local heating supply houses or from neighbors (old house residents around you)) to come and help you out.

      Or at least pay a visit to http://www.heatinghelp.com where you can make the aquaintence of Dan Holohan, and others who frequent that site, who has made it his life's work to maintain the lost art of steam heating. There are some great books available there for dealing with all things 'hydronic' (water heaters, radiant floor heat, hot water heat, steam heat, etc.).

      Steam heat is a wonderful way to provide heat for a home, but its biggest drawback (besides the enormous installation costs, which is no problem for any old house since that part has been taken care of) is that it does require some key basic maintainence thru the years. All too often this has been done poorly, or wrongly, leading to perfectly good systems being wasted or (gasp) torn out to be replaced with (lesser) forced air furnaces (people who love hydronic heat call this 'scorched air' heating).

      If I read your message correctly, the valve that is not working correctly for you is the one that lets the air out but keeps the steam in, and it is stuck in the 'open' position, wasting your steam and your heating money. This valve, and the valves at each radiator, are intented to be replaced periodically and most homeowners don't realize that their crappy heating performance is caused by lack of maintainence, not by any short coming of their basic system.

      All kinds of replacement valves are produced today and the easiest way to get at the instructions of how to do this, and where to get the new ones, is to go to heatinghelp.com.

      Good luck and 'happy hydronicing!'

      PS: I am in no way associated with that web site, but own an old house with steam heat and Dan Holohan's books made a world of difference for me so I try to pass on that blessing to others every time I get the chance.

      1. benraymond | Oct 10, 2002 06:40pm | #3

        Thanks for the info.

        Don't worry, I would NEVER bolt a TP valve closed.  I have a little more respect for the bombs boilers can become if they explode.  This one is opening early.  It's not stuck in the open position.  I just want to know if I need to call a plumber.  Sounds like I do.

        Ben

  2. TLRice | Oct 11, 2002 02:30pm | #4

    Ben,

    First and foremost, if you plan to keep this boiler in service for years to come, get hold of your local boiler service company and have the check it out and perform all required maintenance.I would also suggest that you install (or have installed) some instrumentation on the boiler if you don't have it or is not operable. Outlet/supply temperature and pressure, water level, to start with, a low water cut-off.

    "Do these valves just fail with time?" Yes, just about everything mechanical fails in time, especially those things subjected to high temperatures, water and air. An automatic, level controlled make-up valve would be nice, but not a necessity.

    "Is there something that increased the pressure in the system?" It is possible, but not likely. One pipe steam systems are typically, low pressure steam systems and should have an atmospheric vented accumulator for the condensate (I am familiar with larger systems such as those in old schools and old commercial buildings, and though the opeartion fundamentals are the same, system setup and specialties may differ). Steam traps in the system, if working properly, keep steam from being pissed away out the vent. (These will need to be checked and/or replaced as well.) When they fail, the vent regularly sees steam and can become blocked with various forms of "gunk" (corrosion products, scale, sediment). Pressure in the boiler could be incresed by obstruction in the piping. (Notice any areas that recently started getting less heat?)

    "Can I just wrench the thing off and go to my local plumbing supply

    and buy another valve? Are there standard valves I can use? Is there any chance I'm going to blow up my boiler if I get the wrong pressure relief type?" Find the make and model number of your boiler, operating pressure and capacity and the size, rating and make/mn of the existing valve. With the right information, you should be able to find or order the proper valve. A good plumbing supply house or an old style full service hardware store should be able to get what you need. Grainger carries Watts Regulator brand releifs, plumbingsupply.com has some as well. If the information is not available (most boilers and relief valve have good nameplate data on them), then you will definnitely have to rely on a professional. If you have the information, you should be able to find the proper replacement and install it yourself. It is possible to blow-up your boiler (and a good portion of your house).

    Something else to consider/investigate is the applicable state boiler code that applies. Fortunately, few municipalities, cities or counties have messed with boiler codes of their own. Most states, however, do have a boiler code. If not then the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (section VIII, I think) will apply. The boiler service people will know these documents well, the plumbers may or may not. The code will probably not affect the proper valve selection, but it is a good place to double check.

    Whatever route you choose, make sure the relief is ASME stamped and rated for the service. If it is a hard to find item in your area, consider buying a spare. In power plants that I have worked, replacement and/or testing of releif/safety valves on a regular interval is required. If I had a boiler in my house, I would change the relief valve on a regular basis (like maybe every 8 - 10 years?, this would be something to investigate with the valve manufacturer and/or the applicable code).



    Edited 10/11/2002 7:56:46 AM ET by Tim

    1. benraymond | Oct 11, 2002 10:00pm | #5

      Tim, Excellent info and greatly appreciated.  Thanks.

      Ben

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