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Condensate pump periodically fills system with water

I am a homeowner, and a layman. We have a newish (15 - 20 years) steam boiler and condensate pump installed in a 1908 house in Helena, MT. For our first several years in the house, a couple times a year, the pump would freak-out, pump continuously and push water up into the steam supply lines. I'd either hear it, or notice the house was cold, shut the system down, wait for the water to drain out the relief line coming off the pump, and squeegee it into a dirt crawl space. (One time it made it to the radiators and did $3k in plaster damage.)

Eventually I just shut the pump off, and the problem went away. Though the furnace is higher than the low-point in the return line, water appeared to be getting back to it. I've been running it that way for about 18 months. I suspect there are inefficiencies to having the pump shut off, but it's better than always worrying the basement is going to flood; particularly when I'm travelling.

I would like to bring the pump back on-line. Thinking about starting with new anything that might have resulted in the either the furnace calling for water or the pump pushing water at the furnace. Then doing inspections / preventative maint. every couple months and try to identify a root cause developing before it fails, again.

In reading on this website, I'm wondering if sediment is gumming up floats and valves and the like. If you have any suggestions on how to either chase down a root cause, or just make the problem go away, please share.

Thank you! Bill Shrop, Helena, MT


  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    edited January 2022
    Are you sure you need a pump? Just about everybody's boiler is higher than the low point in the return line since the return is often sitting right on the floor or even below it...that shouldn't matter.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    Odds are you don't need a pump and condensate tank at all... but let that be for the moment.

    The first step is to determine what, exactly controls the pump from the condensate tank to the boiler. There are two different approaches to that. In one, called a condensate return pump, there is a float or other level control in the tank. When the water level rises enough in the tank, the pump turns on and pumps water into the boiler. Trouble is, it doesn't know or care whether the boiler needs water or not, and can quite easily flood the boiler. In the other, the pump is controlled by a level control -- often working together with a low water cutoff -- and turns on when the boiler actually does need water. In that variety, there usually still is a float in the condensate tank -- but all it does is add water to the tank if the water in the tank gets low. The worst that can (and sometimes does) happen with that setup is that the overflow on the tank has to let excess water out onto the basement floor or into a drain.

    So... can you determine what actually controls that pump?

    If it's the low water control on the boiler, it is quite possible -- even likely -- that that control is hanging up or not functioning properly. Can you identify -- or take a picture of -- the low water cutoff? Then we can have a shot at how to maintain it.

    If it's a control in the condensate tank itself, that's a little more difficult to troubleshoot. It could be that that control is hanging up and leaving the pump on -- but it could also be that condensate is slow to return and the tank adds more water --then the condensate returns and the tank adds yet more water, which is neither wanted nor needed.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,060
    You could have an auto water fill on the boiler doing what the pump should be doing.
    But the water returning might be going down the drain not back into the boiler.
    This would mean adding fresh water continuously to the boiler and drastically shorting it's life by the oxygen in fresh water.

    Pictures are needed of boiler and pump from floor to ceiling showing all the piping connecting them together.