3 Weil Mclain boiler sections rotted?

[andrea77]

Ok, so I'm told by the people who installed the boiler in my building (I think it's a wm 80 commercial oil boiler?) three sections rotted and rusted due to excessive replacement water? Weil Mclain (without ever seeing the site, condition-or anything) agreed this was the case.

So-being a non-plumber, I have asked 7 very highly regarded plumbers, and a city inspector if they have ever heard of this....not one has ever heard this in their careers (ranging from 10-35 years). Two plumbers told me there is something on the boiler to regulate the water going into the boiler.

Has anyone ever heard of this happening? Anyone. Thank you for reading!!

[mattbee24]

Well, there is usually something on the boiler to regulate the feed water. BUT, if you happen to get a leak somewhere in the system, that will just keep feeding COLD water into the system.

And that's where the problem is.

Without seeing exactly what you have going on, it's hard to tell. But here is the scenario I think they are referring to.

You have a leak somewhere in the system. As water leaks out of the system, your feed valve lets new water in to keep the pressure constant. The problem is, you are letting cold water into the system. If your Cast Iron boiler sections are hot, and cold water gets introduced to them, there is a good chance they can crack.

The plumbers and inspector you spoke with may never have seen this before, but I have seen it 3 or 4 times in the 15 years I have been in plumbing sales.

Hope this helps some.

[jadnashua]

The typical hot water boiler system is closed. You fill it once, and the water, because it keeps cycling around, eventually gets all of the oxygen, minerals, etc. cleaned out or at least stabilized. If you have a leak, you are introducing additional oxygen (which will be disolved in the water), along with other stuff. If you keep adding oxygen to iron, and let it get hot, it rusts. It can only rust if there is oxygen. If there are no leaks, it stops rusting pretty quickly. If it continually leaks, it will continue to rust. Do that enough, and there's no iron left...

[nhmaster]

I assume this is a commercial steam boiler yes? If so, steam boilers do typically require make up water at periodic times. However a tight system should not require massive amounts. What is probably happening is either you have leaking wet returns and or bad F&T traps and main vents that are allowing too much water to escape the system. If it's a hydronic system, low return temperatures can cause the boiler to condensate. the condensate is acidic and can rot the boiler.

[patsfan78]

Your leak my have been in the block itself or maybe in the piping. In this case since the block is already ruined, I hope the leak was in the boiler. O2, minerals, condensate, they are all bad things to a big chunk of cast iron.
Keep an eye on your stack temperature, to make sure it is at the appropriate temp for your setup.

Good luck,
Mike
http://www.hitechheat.com

[MechanicalEngineer40years]

Even thought this is an old thread, I came across this looking for cast iron boiler section failures in an investigation that I am currently involved in. Cast iron boilers don't rot. What most often happens is one of two things that cause cast iron sections to fail. Before I continue, excessive make up water due to what ever reason will cause tube failure in steel boilers and some may will call this "rot". Cast iron sections will fail due to the introduction of cold make up water into a dry (water absent from the boiler sections itself) and the boiler has been "dry fired". This is why they have low water cut out controls on water and steam boilers. This type of failure is common on cast iron steam boilers when the water level control is not working and make up water is added by "hand" to a red hot boiler. Just like adding water to a car engine when it has overheated and you are not willing to wait for the hour or two to let the engine block to cool down. You will crack the cast iron block. Steel boilers will not do this, they have a much greater coeficient of expansion.

The other issue that brought me here in the first place is one much more difficult to diagnose. Boiler section failure in exactly the boiler type and manufacture of the one above. These sections are used by a few manufactures as not many foundries exist in the US any more and a number of different product lines use the same castings. These particular cast iron sections fail usually in the middle sections. The boiler is standing by "hot and satisfied" with no call for heat and is satisfied lets say at 180 deg f. No water is circulating. A zone calls for heat that has been sitting idle all afternoon on a sunny, mild winters day. The sun is setting and the zone now calls for heat. The pump starts, no 3 way modulating control valves are on this zone. Just a pump with a large amount of piping and radiation, or maybe a very large coil in duct work (again with out a 3 way valve), This huge slug or flow of relative cold water lets say 75 deg f. water hits this 180 deg f. water that is not mixing well creates a condition called thermal shock! Cast iron can not expand/contract quick enough and the cast iron gives in the only way it can satisfy this need to move and something must give. The cast iron will crack.

The "job" I have in mind had steel boilers which never had a problem and a contractor decided that cast iron was the correct replacement choice. I have seen jobs that cast iron replaced cast iron and for the first time sections started to fail due to thermal shock. Why not the other or original boiler? Water flow design and quality and thickness of the castings themselves. Solutions do exist, they can be found in a number of changes and modification to the way the piping is to be made up for these boilers. To my knowledge they are in the at least the 3rd generation of modifications to rectify this issue.

Now whats important to me. I would like to hear from anybody who has had repeated/ongoing commercial boiler section failures and can give me the correct and detailed data to include but not limited to the boiler model and manufacturer, number of sections, burner type and fuel, steam or water, age and application. I in turn will help you correct failures with suggestions to correct the issue and suggestions to aid you in dealing with the legal aspect of this defect. Thanks for your time.

[BadgerBoilerMN]

So you think 75° return water is cold and can't understand why replacing a steel boiler with a cast iron boiler on with the same near piping would lead to leaking sections and you're going to help us how?