Busted Boiler

How about a seasonal topic, like a busted boiler?

Our Trinity LX150 by NTI (NY Thermal Inc.) started hammering and banging and eventually shut down. When I checked the boiler display, I found an error message saying: “Lockout 81 – Delta T limit”.

At the time I had no idea what the cause of the problem could be. So I started with the troubleshooting chart in the operation instructions, which was pretty straight forward:

I tested “Fuse A” and it was fine. I checked the pump, and it was running. The plumbing was correct too and I had water pressure of 20 psi. That left me with the dreaded last option: a fouled heat exchanger. Dreaded, because I wasn’t quite clear on what it meant and what the implications were. After some research and scouring through YouTube, I finally was able to put the pieces together.

A boiler doesn’t just break. It usually has a good reason, such as deferred maintenance. And I am embarrassed to admit that I am guilty of such deferral.

Our high efficiency boiler (Trinity LX150) takes care of our domestic hot water and hydronic heating system. I wrote about our mechanical system and how it functions in a previous blog post, which makes for good reading.

The boiler has a modulating capacity from 25,000 to 150,000 BTU and a stainless steel heat exchanger.

It is that heat exchanger that makes these boilers so efficient. In our case, we have small tubing (probably 3/8″) that surrounds the burn chamber. The ratio of the small water volume in the heat exchanger versus the relatively large surface area of the heat exchanger allows for efficient heat transfer.

But this efficiency comes at a price. Because of the small diameter, the tubing can be prone to clogging by lime and other mineral deposits. And once deposits build up inside the heat exchanger tubing, the efficiency of the boiler goes down and the banging and hammering starts.

If the water in the closed loop hydronic system would be treated properly, the risk of mineral deposit formation would be greatly reduced.

When our installer first filled the hydronic system, he added an additive that depletes the oxygen in the water and reduces the risk of corrosion and mineral deposit formation. From that point on, the closed loop system was supposed to run almost maintenance free, as long as no new water (i.e new oxygen and minerals) was added to the system.

Read also: RPA – Chemical Water Treatment

But I did add new water. First when we filled and started up the radiators on the 1st floor, and again later when I partially drained the buffer tank to service a sensor. I did not think about the newly introduced water at the time, and it came around to nip me in the butt!

The first symptoms were the hammering and banging in the boiler. I assume what happened was that the tube diameter was decreased by mineral deposits to the point where the flow volume was so small and slow that the water turned into steam. That’s a very unnerving thought!

The boiler has an amazing array of safety sensors and mechanisms. It recognized the dangerously high temperature in the heat exchanger and automatically shut off.

That is good for safety, but it is not good for maintaining domestic hot water and keeping the radiators running.

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About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

One thought on “Busted Boiler

  1. I am impressed (but not surprised) by your matter of fact, straight forward analysis of the fouling, the reasons for it and the effects on the boiler, its reduced performance and fail.

    Closed water systems are not that often really closed (I learned that the hard way in a destillery some years ago…) refilling with unsoftened water is adding hardness – measured in degrees german hardness [°dH] – which will settle as calcium- and magnesium salts on surfaces at temperatures above 70-something °C. These salts have a poor solubilty in water, which is reason for the fouling. CIP (=cleaning in place) with warm acid solutions can be used to clean the fouled surfaces, a standard procedure in some industries to regain proper heattransfer. However the use of acids demands propper handling with a keen eye on the MSDS (and at least googles on the eyes! – you only have two!). To give the acid access to the salts it is necesssary to have flow through the heatexchanger, without thoughflow the chances to clean are rather small.

    Looking forward to learn how you “solve” the problem.

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