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Steam Boiler overflowing

I am having a problem with my steam boiler that I have never had in the 12 years that I have lived in my house. the boiler keeps flooding for no apparent reason.

I have a single pipe system with wet return.

The system worked fine last season and when I shut it off in late April the boiler had a normal water level.

when I tried to fire up the boiler last week as a test it did not turn on. I called a service technician and they diagnosed that the boiler was flooded with water and therefore didn't fire up. we had to drain the boiler for about 15 minutes to get all the extra water out!! the technician said that he had never seen a boiler add this much water but the tech could not find the source of the water. he checked the water feeder and it wasn't leaking. he had no other idea where the water could have come from.

for the next week I checked the water level of the boiler several times and it was steady and wasn't adding water so I thought this was a one time problem. the last time I had checked the water level was yesterday morning.

this morning however I fired the boiler on and after about one hour of use I saw a lot of muddy water coming out of a radiator very close to the boiler room. I ran down to the boiler room and saw the water level above the maximum on the gauge. I turned off the boiler and started draining water and it took me about 5 minutes of draining to get back to a normal level.

so here the mystery. for the last week when idle the boiler didn't att any water at all and suddenly once fired up it overflowed within an hour. and why did the water rise to a level to start gushing out of a radiator?

any guesses what could be going on? any help is greatly appreciated!


  • Gary SmithGary Smith Member Posts: 328
    try turning off the automatic water feeder or shutting the valves on both sides of it to prevent inadvertent water feeding, then observe.

    Does your system also heat your hot water?
  • JUGHNEJUGHNE Member Posts: 7,198
    What type of water feeder do you have?
    Pictures of fill valve and piping would help.
  • wanttolearnwanttolearn Member Posts: 59
    Here are two pictures one of the water feeder and the other of the piping.   It pipes straight into the wet return from what I can see
  • JUGHNEJUGHNE Member Posts: 7,198
    You need to back up for the pictures. Need to see piping and valves from floor to ceiling.
    Also any controlling devices for water fill.
  • wanttolearnwanttolearn Member Posts: 59
    Hard to catch everything in one picture.   There is a **** off valve right before the watier feeder and then after the water feeder the pipe turns up and over to the wall where it then goes down into the wet return.   Here are some more pics.  The white painted vertical pipe into the wet return is connected to the water feeder.
  • JUGHNEJUGHNE Member Posts: 7,198
    As asked how do you heat your hot water for the kitchen etc. ?
  • wanttolearnwanttolearn Member Posts: 59
    It’s a different hot water heater.   Has nothing to do with this boiler
  • JUGHNEJUGHNE Member Posts: 7,198
    The only water can get into the boiler is thru the auto feeder or a faulty by pass valve if you have one.
    How do you add water to the boiler manually?

    The auto feeder may not shutting off completely or is being controlled by a bad LWCO signal.
  • JUGHNEJUGHNE Member Posts: 7,198
    You had this problem 6 years ago.
    How did you fix it then?
    Your LWCO probe may need cleaning or the entire control replaced.
    Have you cleaned the pigtail and sight glass ports into the boiler?
  • wanttolearnwanttolearn Member Posts: 59
    Don’t remember this exact problem think it was something different a few years ago but thanks for the tips let me look into some of these suggestions! Appreciated.
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