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Steam boiler shuts off on low water after 48 hours

Our Weil-Mclain EG-45-PI steam heat boiler has this season started to run out of water after only 48 hours when the heat is on.
I've had our plumber and a steam heating specialist come and look at it and they both say that the boiler itself looks ok (it was installed in 1987).

I also did a check by turning off the heat for two days, overfilling the boiler to the top, and then checking after two days, and there was no water leakage at all. So it only loses water when the heat is running. It's a gas heat boiler if that matters.

I've looked at the very useful "Steam Problems?" Q&A section on the site.

The steam heating specialist who came in said that as the boiler itself looks to be ok, the next step is to replace the air vents that are old.
If that still doesn't fix it, he said the next step is use pressure gauges on each of the radiators to try and isolate the problem.

Would it help to narrow down this problem if I shut off individual radiators, one or two at a time and then see if that points to a particular radiator?

Also, how can I tell where the return line is? I believe my radiators have only one-pipe.



  • Fred Harwood
    Fred Harwood Member Posts: 261
    low water

    One-pipe steam uses the one pipe for both steam and returning condensate. If you find no water or steam leaks in the boiler or the piping, the next likely culprits are the radiators, radiator valve stem packing, and the vents, which may not be closing when the steam arrives.

    You need to inspect each component carefully, and ensure that each radiator valve is fully open. Tell us what you find.
  • Fred Harwood
    Fred Harwood Member Posts: 261

    Make sure you check the end-of-main vent as well.
  • Steamhead
    Steamhead Member Posts: 16,832

    look to see if any return lines are buried. If they are I'll bet they're leaking.

    Also, if you see a white plume of vapor coming out of the chimney while the boiler is running, it's coming from a leak in the boiler. Sometimes these leaks only occur if the boiler is hot.

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