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Residential steam boiler keeps flooding up to 20 gallons. Help!

American Standard boiler keeps over filling up to 20 gallons - we've read every blog post, and have tried troubleshooting but nothing is solving the flooding issue. The low water cut off valve is new, and the automatic fill device works. No noticeable foaming. Near boiler piping has been in place for many years and works fine. Why else could this be happening? We are desperate for help/suggestions.


  • Fred
    Fred Member Posts: 8,542
    Is there a tankless hot water unit in the boiler? If so There is probably a leak in the coil that is filling the boiler. If there is no tankless coil, shut the water supply off tyo the auto fill unit. It may be working but it may also be letting water pass through the valve.