The case of the rusted boiler, this Friday's case

RayWohlfarth

In this case, we sold three hydronic boilers for a school district. After ten years, the boilers were destroyed. Looking inside, the tubes were filled with rust. The system is a two pipe system which uses hot water in the winter and chilled water in the summer. The piping has a summer winter three way valve to isolate the boiler or chiller. I will let you know what we discovered to be the causes. This case has two causes for the failure of the boilers.

ratio

The valve failed & wasn't isolating the boilers from the chilled water. Maybe low return temps as well?

mattmia2

Lack of a flow check or something else that would prevent gravity flow on the non 3-way valve side so the boiler was getting chilled and sweating.

clammy

How about thermal migration due to using only a three way value while in crossover for cooling ,that and possibly constant flow w no low limit temp control durning the heating season meaning constant flow reguardless of weather the boiler is calling or not . I ve seen this when multi boilers are installed and a house pump provides flow for all boilers usually a tekmar is used for cycling the boilers on a swt .
Close peace and good luck clammy

HomerJSmith

What's wrong with that boiler, looks fine to me. Oxygen ingression??? Bad wawa. There is a higher concentration of oxygen in cooler water than hot water.

retiredguy

I won't add to the answers shown above since I am late to this party and everybody sees what happens in a poorly designed system. I will say however that most of the problem stemmed from a heating engineer that skipped a few classes on using water for both heat and A/C. I saw this same problem on most systems that used a 3 pipe system instead of a 4 pipe system or anytime they tried to retrofit a heating system the cheap way by adding a third pipe to supply chilled water for the A/C. If you are going to utilize a 3 pipe system instead of a 4 pipe system make sure that all the isolation valves work and actually seal off all flow and that the custodian or stationary engineer of that building understands just what valves need to be switched. That is my guess for the first problem and for the second problem I will say that they could have had a draft problem, poor burner combustion or too low a minimum flame if they were using a low-high-low or a full modulating burner.

GGross

pump and dump chilled water system likely, too much fresh water even if the boilers were isolated they would take on those fresh minerals each season when they switched back to heating. 10 years of yearly water changeouts without proper treatment will do that. Saw this happen at a ski resort with 4 triangle tubes, we ended up isolating the boilers with heat exchangers so at least it was a less expensive and quicker replacement when they rotted out

RayWohlfarth

Greetings all @ratio caught both causes first. The 3 way valve was leaking chilled water into the boilers during the summer and they condensed, a lot. In addition, they set the boiler water temperature for 140 degrees F and denied doing it. I think about this job and thought if they had a boiler expert come in once a year, they could saved all this aggravation and money. A yearly service call would be much cheaper. You can see the moisture damage from the chilled water on the pipe insulation. thanks

RayWohlfarth

Ooops forgot to post link to new videos, The case of the rusted boiler and the Detective Tools Hydronic boiler safety controls
https://youtube.com/watch?v=MPrisYhN_7k

https://www.youtube.com/watch?v=U4I7HGlKOJs

Solid_Fuel_Man

Yeah....I'll take a large pepperoni with extra rust please. Can I get that delivered? Be sure it's cooked over a gas flame please .... low, hi, low.....