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Weil McLain Boiler Leak

Tjm Member Posts: 2

I have a Weil McLain boiler that heats my hot water/baseboard radiant heat for my house on 3 zones. It is the original boiler installed when the house was built in 1999. Two years ago I replaced the pressure relief valve, fill valve, and expansion tank. I have started using heat again for the season approximately one month ago. The system seems to be working fine, as I am getting heat in all zones and getting hot water. Today I noticed a small leak coming from the bottom of the boiler. There are no obvious valves in this location that point to exactly where the leak is coming from, but it is dripping water to an extent that raises concern. With winter around the corner, this is not something I’d like to delay on only to find myself dealing with it in freezing temperatures. I am by no means certified to be diagnosing or conducting a major overhaul of a serious nature but am capable of routine maintenance, valve replacement etc. I am hoping to gain some insight into why this would occur or to seek some advice on whether or not a replacement system is what I should be focusing on. Attached are some pictures that may be helpful in diagnosing. Thank you!


  • nde
    nde Member Posts: 86
    Need a pro asap to check. Either the boiler is failing near a seam or that hot water coil is leaking down into the chamber the out the door front. Can you see water coming down from the hot water coil? 23 years is a little early but better than many if it has failed in the block vs the coil. Coils that old can be a real pita to fix.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,572
    edited November 2022
    That boiler has a limited 20 year warranty on the cast iron sections. That warranty is pro-rated, Pretty much worthless today!

    There are 2 possibilities. That water leak at the bottom could be coming from the DHW coil gasket, traveling inside the yellow/cream color metal insulated jacket down to the bottom. The other possibility is that a cast iron section is cracked and the water is leaking inside the fire box (behind the black burner door) and leaking out thru the door gasket. If it is the gasket or the tankless coil, that can be fixed without replacing the boiler.
    If it is a cast iron section then you can get a new boiler. or a new cast iron block, and keep all the other parts. The second choice may actually cost more because someone needs to be paid to remove all ... YES ALL!... the parts from the boiler block and then reassemble them on the replacement block. That will add at least 6 hours to the project. Weil McLain still offers the WTGO boiler but it is a different series. You may be able to purchase the boiler less burner for a little savings. Or you could go for a completely different brand of boiler.

    The trouble is... Cast iron boilers are scarce now. You should get on someones list for a new boiler, If you need one.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    EBEBRATT-Ed Member Posts: 15,329
    Is that leak near the burner door? If it is it could be just condensation from a cold start. Does the leak stop when the boiler gets hot? If it continues with a hot boiler then you have an issue for sure
    HVACNUT Member Posts: 5,751
    Is that leak near the burner door? If it is it could be just condensation from a cold start. Does the leak stop when the boiler gets hot? If it continues with a hot boiler then you have an issue for sure
    It's got a tankless coil with a triple aquastat. The block is always hot.
  • Tjm
    Tjm Member Posts: 2
    Thank you for all the responses. The leak became pretty significant to the point it was losing about 2 gallons/hour leaving me to shut it off and turn off the feed to it. It’s hard to pin point where the leak is coming from exactly, but it appears to be coming out of the door gasket. I have someone coming to look at it later today and am ready to accept the fate of having to replace the boiler. I appreciate the insight everyone has offered and will update upon diagnosis. With that said, if I do need a new system I’d like to do a complete overhaul as the previous owner has the plumbing poorly managed with various pex , sharkbites, and crimped copper which is an eyesore. It is heating a bi-level house that is approximately 2100sqft. Is there a quality unit or system one could recommend that is well accepted in this industry? Not looking to cut costs on something as vital as a heating system.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,703
    That boiler uses O rings between the sections rather then push nipples ... O rings leak over time ...
    I have enough experience to know , that I dont know it all
  • dirtbike59
    dirtbike59 Member Posts: 8
    My friends Weil McLain just let go at 11 years the casting sprung a leak. He got forced into buying a new unit cause there are no parts available right now. Under warranty sure but that’s only as good as the parts availability.