Leaking, probably cracked Weil-McClain boiler - good replacement options for old house?

[Ryanarin]

20 years ago when I bought my house (built in 1919) it had a huge, ancient hot water boiler covered with asbestos, that had been converted from coal to natural gas. I now wish I still had the thing (minus the asbestos).
In 2005, silly me thought it might be a good idea to replace it, even though it was completely reliable. I got a new "efficient" (!) condensing Munchkin boiler- bad idea. That gave me nothing but trouble, failing randomly because the sparker didn't work, among other things--it was the worst thing I have ever bought. Well, maybe.

In 2010, after I was told the Munchkin's heat exchanger was clogged with minerals/rust, and after the PRV had failed and flooded the basement, I had a different plumber take the thing out, and install a Weil-McClain cast iron boiler-- believing it would be able to handle my old radiators better.
Within 2 years of the new installation, the boiler system pressure was dropping daily-- the plumber who installed looked at it and when he heard the slow drip coming from under the boiler he groaned...it had a cracked section. He took the boiler apart and tried to get the cracked section replaced by W-M. They said it had clogged with mineral scale, (in two years since installing!) and that voided the warranty. So, he put in a replacement cast iron section, put the boiler back together, and I paind the cost for this repair ($1600).
It worked well for 2 years, so I thought it was money well spent. Nope!

The same issues (dropping pressure, dripping sound under the boiler but no visible water) reappeared last winter. I have been adding water to the system since then, and looking for signs of a leak somewhere else... two other plumbers have checked out the crawl space and the radiators to look for leaks there, and not found a thing. Under the boiler is dry--so the only sign of the leak is the sound of a drip. Also there is a squeal/hiss inside the boiler sometimes when its heating.

The plumber who installed the W-M has left the company, but his helper has taken over and says he can take it apart and replace a cracked section again, if that is the culprit. He also said he could add Fernox Leak Sealer for the time being, to see if that helps. I am leary of that stuff. On another online forum someone says that adding anything petroleum based to a W-M boiler will destroy the gaskets or o-rings.

So, should I just replace the boiler again, instead? The Weil-McClain is very reliable in other ways compared to the earlier munchkin, no problems aside from having to add water to bring up the pressure. I add about 4 psi every 2-3 days, to bring it up to about 14 psi. It seems to lose the most water when its cold, I have noticed.

When I read some of the problems people have with boilers, I wonder if I would again just be buying a whole new, different set of issues, if I replace it. I don't care at all about efficiency, considering I have spent an extremely inefficient 12k for two different boilers that don't work well, compared to the ancient original one.

If I should just replace, are there any recommendations for a simple and reliable, if not very efficient, boiler for an old house with lots of rust/mineral sediment in the pipes?

 

[Dana]

Since you have a heating history on the place, the first order of business while looking at the leak would be to run a fuel use heat load calculation. The original boiler was most likely ridiculously oversized, and the W-M is probably sub-optimally oversized.

Then measure up the radiation, zone by zone to see if your place is even a good candidate for a condensing boiler.

Is it big high-volume cast iron radiators, or something else?

A lot of people had problems with the Munchkin, don't know all the details. There are lots of installer-errors that could lead to early failure, as well as manufacturing design issues. But new stainless steel fire-tube modulating condensing boilers are quite a bit better than the goods being sold a decade ago, even some of the cheap ones, and they're more forgiving (but not completely idiot-proof) for the less-than-perfect installation in systems previously heated with a high mass cast iron boiler. They can take higher flows, and don't usually need primary/secondary plumbing to work, and can be a fairly easy drop-in replacement. Some of the cheaper ones are CHEAPER than equivalent output cast iron, and DIY-able with a bit of design guidance.

The W-M CGa series boilers are dumber than a box o' rocks and pretty reliable overall. But if it's leaking it's not worth owning. If replacing it with cast-iron, the Burhham ES2 series and ESC series are pretty good, and are internally plumbed to be tolerant of low-temperature return water (down to 110F), which can be an issue if you have a high-mass radiation. (If the W-M is toast it could be due to low-temp return water condensing on and corroding the plates. A competent boiler installer would have designed in the protection for that, using one of a handful of approaches.)

If the leak isn't in the boiler, it's not worth replacing it, but rebuilding it with a new plate (if that's what's leaking) on-site is a waste of money. If a dose of Fernox slows it down, great, live with it. If not, the water is going somewhere, and if it's going out the exhaust and only leaks when the boiler is at high temp it could take awhile to find the leak, until one day you find the puddle of steaming water in the boiler room.

 

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[Ryanarin]

Thank you so much for your super helpful reply. I really appreciate this great information. Yes, they are big high volume cast iron radiators--the largest is 32" x 38" x 10". Others (7 more) are smaller.

Then Fernox is safe to use with this boiler? I guess that is what I will try first, if so.

(If the W-M is toast it could be due to low-temp return water condensing on and corroding the plates. A competent boiler installer would have designed in the protection for that, using one of a handful of approaches.)

This tells me a lot. Does setting the thermostat back at night have an effect on the return water temp? I put a programmable thermostat in the house shortly before the second time the W-M leaking started, and generally set the thermostat down from 68 to 62 degrees at night. In the morning, its first heat is to 65 degrees, then back to 68 after 2-3 hours.

Could you give me any more details about the approaches you would use for protection for low temp return water?
Wondered also-- when the W-M was installed, they decided to vent it through the chimney, instead of using the Munchkin's horizontal pvc venting. This 5 inch piping from boiler to chimney still looks brand new, zero signs of rust etc. But the gas company told me that piping should have been sized smaller, to prevent cooling condensate in the chimney coming back and damaging the boiler. Could that cooling condensate do this corroding damage?

 

[Dana]

The thermal mass of the water in the rads means it takes awhile for the return water to rise to a safe-ish 130F+, even with a pretty big boiler behind it. When the space heating load is low, even water entering the radiators at 130F might overheat the place. (I heat my whole place with 125F water, even in the dead of winter, but that's by design.)

The most common solutions is to install a bypass branch near the boiler to mix direct boiler output with the return water, raising the entering water temperature (EWT) at the boiler to a safe, non-condensing temperature. It usually has a either a ball valve on the branch to hand-tweak the EWT to something non-condensing, but some will have a thermostatic mixing valve for that purpose. A similar approach is a "system bypass", which is a bit safer from a condensing perspective. The difference is basically which side of the pump the bypass branch tees into.

With a picture of your near-boiler plumbing it's possible to figure out if something like that was installed, or if some other measures were taken.

If it was being pumped direct with no bypass, it's almost certainly been condensing. That's good for efficiency, but TERRIBLE for the lifecycle of a cast iron boiler.

If your boiler needs a 4" stack, that means it's a CGa-25 or a CGa-3? Which is it?

If you had oversized venting with chronic condensing in the flue coming all the way back to the boiler you'd probably see signs of seepage at the connection points (or the draft hood on the boiler).

Low temp return water is great for condensing boilers, but getting the pumping correct for both the boiler and the high-mass radiators can require doing the math. You can't just pump most mod-con direct with a 1/4hp behemoth the way you can with most cast-iron, but you probably don't really need a monster-pump either if running continuously at low temp with a mod-con under outdoor reset control. Most systems are over-pumped.

 

[Dana]

DO take the time to measure and add up the total effective direct radiation (EDR) square feet of the radiators, and compare the DOE-out BTUs on the boiler nameplate to the total EDR of the radiators. If the ratio of output/EDR is <100BTU/EDR-ft^2 the condensation hazard is much higher than if it's a more typical 150BTU/EDR-ft^2 or higher. But that very risk would be of huge benefit with a condensing boiler.

Also take the time to run a fuel-use load calculation at the 99% outside design temperature (+11F for SLC, and yes I know it gets a lot colder than that during cold snaps, but that's not the point here). If the ratio of the 99% heat load/EDR-ft^2 is 100 or less it makes a condensing boiler a lot more desirable than if it's well north of 150BTU/EDR-ft^2.

 

[Flat_Twin]

Sounds like the hard water issue needs to be addressed. Start by having it tested with hydronic heating in mind.

 

[Ryanarin]

Thanks very much for this reply. Sorry for the delayed response-- didn't seem to get notifications in my email. Happy New Year!

Looking at it myself, I don't think the return water to the boiler has any kind of bypass.

Here is a photo showing the piping, which was originally put in with the earlier Munchkin condensing boiler. This one (W-M gold CGi -4E) was installed into the Munchkin piping when it was replaced.

If you can see the piping system from this photo, I would love to know if the return water is set up so it comes in too cold. (Or if a closer photo is needed.) Off to the right of the photo, the water heater is a second zone for the system --that's what the second pump leads to.
Could a crack in the cast iron plates happen from cold water coming into the boiler return?


Thanks for the link to the document showing how to measure radiator heating capacity. I was confused by my radiators They look reversed compared to the drawings shown there.

Most are seem to have three...tubes or columns?



A few are another type, (newer?) with 6-- tubes? (Below)



Thanks again for your helpful advice, I am definitely learning something here.

 

[Dana]

I don't see any bypass branches or a hydraulic separator (which would have been necessary for the Munchkin, but perhaps removed.) Take a cooking probe/meat thermometer and tape it to the return plumbing close to the boiler and give it a wrap of fiberglass insulation. If it's much under 130F during normal operation it's a problem, and if it's under 125F it's a boiler-killer.

I also don't see an expansion tank in the picture, usually mounted on the bottom side of the air scoop (the black thing in the upper left corner with a bronze vent mounted on top. The boilers have a port for a closed type overhead expansion tank next to the output port on the top, but it doesn't seem to be plumbed in either. (See p.17 of the manual.) There has to be an expansion tank of some type somewhere on the system, but it's not in the picture.

The distinction between "columns" vs. "tubes" in that radiator size estimator document is that when viewed on end columns are >>2" wide, whereas tubes a <<2" wide. If you compare your radiators' dimensions to a radiator that is still being manufactured, the manufacturer's EDR specs should be pretty close. (Physics doesn't change much with age. )

Burnham radiators
http://governaleindustries.com/products/
Governale radiators

OCS radiators

 

[Ryanarin]

Thanks for the info. The expansion tank is hard to see, its silver, facing away. Its in the upper left. A few plumbers have knocked on it recently, saying it seemed fine. The other problems, did not seem to occur to them! So glad to have gotten such good feedback here, thanks again. Now for some tests and math.