Clogged Steam System

One of the common steam heating service calls we get dispatched to are steam heating systems that are not working properly. Homes in northeast United States typically have an oil or gas fired boiler – either hot water hydronic or steam and Pipe Doctor Plumbing, Heating, Air Conditioning (and now) Refrigeration technicians often get called last (when other plumbing contractors have failed) to tackle the job. As a company that specializes in service and repair, we have a great deal of knowledge, experience and expertise working on these types of systems. The job recently competed as detailed in the rest of the article is no different.

Last Friday we were called upon another frustrated homeowner in Valley Stream who was tired of “amateurs” attempting to fix their gas fired Weil McLain steam boiler. The first plumber replaced the steam radiator air valve what continuously sprayed water into the room. They essentially “masked the effect” but didn’t resolve the “cause” of the problem (since the new air valve sprayed out water a few hours later). Plumber #2 closed the radiator valve and said the radiator was clogged. The next day the main air valve at the end of the steam main in the finished basement flooded the basement with gallons of water – and took down a large section of drywall ceiling in the process. Plumber #2 returned the following day and said the boiler was flooded. Drained the boiler and, yup you guessed it, the issue returned later that evening.

Any good technician asks questions and listens. A homeowner can usually give the tech a wealth of information. Because that’s what we are trained to do. Listen. Diagnose. Resolve. There is no guessing. (I’m not saying we get it right 100% but we do resolve 100% of our clients issues).

In this example the issue was obvious. On this steam system the rear wet return was clogged. Just like a clogged shower or sewer main it prevented condensate (water) from returning back to the boiler. With nowhere to go it sat at the end of the wet return slowly filling up the drop from the end of the steam main and as steam, rushing from the boiler at 40+ mph, forced the water out. Anywhere it could. It went out of the steam radiator air valve and the steam main valve. At the same time the water was violently exploding (since it was expanding 17,000 times) as that steam hit it causing severe water hammer. No Mr. & Mrs. Homeowner, your home is not possessed by demons. (We had an elderly couple the previous week who really thought that)

The solution unfortunately wasn’t so simple in this completely finished basement. With the exception of the boiler room, none of the piping was visible.

Here are the steps we took:

  • (1)Using our Flir i7 thermal imaging camera we traced out all the steam main piping and wet return drops.
  • (2) We carefully opened walls and ceilings to expose piping we needed to access (cleaning up all debris in the process).
  • (3) 80 year old steam piping isn’t easy to take apart, but with experience comes know how. We cut and disassembled piping to cut in new isolation valves and drains on both wet return drops.
  • (4) We cut and disassembled the wet return immediately before the Hartford Loop to install another set of isolation and drain valves.
  • (5) Carefully using pressure regulated domestic water (with a check valve) from the water heater drain valve we flushed out each wet return removing tons of debris. Kind of like low pressure water jetting, until the return piping was clear and clean.
  • (6) We flushed and drained the boiler multiple times. Also removing nasty debris that can interfere with heat transfer, clog up the pigtail, fowl up the low water cut off, etc. And finished up with treating the boiler with steam boiler chemicals.
  • (7) No job is complete without a combustion and draft analysis, usually done after cleaning out the main burners and combustion chamber. Printed the results, with date and time, and attached a copy to the front cover of the boiler.

End result? Another completely satisfied homeowner with a quiet system. We advise all homeowners to have their heating systems inspected, tested and cleaned annually by a reputable, experienced and knowledgeable plumbing and mechanical contractor. Steam boilers should be flushed out monthly during the heating season and the wet return should be flushed out annually. See our other articles for information on how and why this is very important on steam systems.

If you are within our service area we’d welcome the opportunity to service your property. Give us a call at 516-348-6300 or email us at If you are outside our area check out HERE and HERE for a referral to contractor who can help!

Disclaimer: This article is for informational purposes only. Do not attempt to tackle a job like this yourself unless you are a skilled and experienced plumber. Under no circumstances attempt this on a weekend, late in the evening or on a major holiday. You can become royally screwed and end up without heat. Yup, your wife will yell and likely divorce you! (Especially after the plumber visits and gives you the bill!) Just Kidding! Laugh now then check out our YouTube channel. While your at it, visit us on Facebook and ‘like’ our page. Thanks for reading.

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