One of the best and worst things about hydronics, and arguably any HVAC system, is that a system can be really screwed up and still work well enough that no one would complain about it. Think about how often you walked in on a job and wondered how it ever worked. In many cases, those systems have been “working” for years!

No worries; all you need to do is convince the customer that the system he paid dearly for is installed incorrectly and provide a quote to fix it. This is where I would usually start the conversation with some leading questions: “Besides this current issue, how has the system been working for you?” or, “I see this is our first time out; were you looking for a second opinion or was it our company’s awesome roadside inflatable flailing arm guy that got you to call us?” 

Hopefully, you can help them realize that the boiler’s multiple, full-service record stickers are not normal.

This month, I will walk through a few of the jobs I remember fondly, even after eight years out of the field. Sometimes the problems were corrected; other times, not so much. In either case, I dutifully documented these wonders of the world on my invoice. And I learned from them as well.

Parallel-flow Piping

The first job was a high-efficiency boiler installed in an older system converted from gravity circulation. This system had a ton of potential; the home included extensive envelope upgrades and retained the beautiful cast-iron radiators. Since the home’s heat loss was reduced significantly, this allowed those radiators a chance to operate at much lower temperatures and take full advantage of the boiler’s ability to condense. 

One small oversight: The boiler circulator was pumping into the supply outlet of the boiler. This meant that the sensor tasked with reading the supply water temperature was reading the return temperature. The problem here is that, typically, heat exchangers are set up in a counterflow configuration. This means the cold return water enters the heat exchanger at a point where the combustion gases are leaving and at their coolest. 

The way this system was piped is referred to as parallel flow. This severely limits the heat transfer capabilities of this boiler.

As crazy as it seems, this system worked and saved the customer a lot of money on utility bills compared to the old system. We called the manufacturer; it confirmed that the system would work like this, but highly recommended correcting the piping. In the end, the piping was corrected. The boiler was much happier and was even more efficient. 

Undersized Boiler

The second was a junkyard and auto repair shop. I was called out to diagnose an underperforming hydronic system in the shop as it wouldn’t keep up on those cold days. The cast-iron boiler with an air of DIY was connected to a single loop of soft copper buried in the concrete. 

I started asking questions; it turns out the 15-year-old used boiler was installed a year and a half before my visit. It ran well the previous mild winter and replaced a wood-fired boiler the owners were sick of feeding.

With the aquastat set to 190 degrees and the boiler gauge barely hitting 120 degrees, I did some quick math to realize the boiler was wildly undersized. Being a phenomenon not usually seen in our industry, I did the math again to double-check my hypothesis. 

This was a case where the system reached thermal equilibrium; the boiler was producing all the heat it could and the slab was taking all of it. There was nothing I could do besides call Guinness to document the world’s first undersized boiler.

Given the poor design of the system and the copper buried in concrete that was living on borrowed time, I recommended abandoning the system in favor of another solution. The owners didn’t like my idea, citing that the system worked great the previous (very mild) winter. After much conversing, I took a note from Kenny Rogers playbook and decided to fold ‘em. 

Believe it or not, I didn’t make their Christmas card list that year or any year since.

Combustion Gas Recirculation

The third was a high-efficiency boiler in a home having some trouble. The first sign was the note on my service ticket; “Customer selling home; keep costs to a minimum.” It never ceases to amaze me how much of a curse such a note is. 

To start, the boiler was having some ignition problems per the control. After reaching around to remove the cover, I found it had some aftermarket ventilation installed. You could tell this was due to heat, given the discoloration of the plastic.

Digging a little deeper, I found the aluminum heat exchanger had failed, allowing combustion gases to kiss the cover noted previously. Before you say anything, units with aluminum heat exchangers were prevalent in the area and had a good track record. So, despite what you may have read or experienced, they’re not all bad. 

This poor boiler was a victim of its installer. On top of the failed heat exchanger, the flame sensor was trashed, and all the plastic components within the boiler jacket were one sneeze away from crumbling to pieces. 

This is where we need to realize that the problem isn’t always what it seems on the face of it. Something started this domino effect: the recirculation of combustion gases back into the boiler’s fresh air intake. 

The intake and exhaust terminations were positioned in an inside corner and, despite their best efforts, were still recirculating when the wind was just right. Coupled with the low exhaust velocity of the combustion gases on modulating equipment in low fire, this is what you get. 

In the end, I did keep the invoice low as they only paid for the service call at that time. However, the invoice for the new boiler was not so low.

The moral of these stories is that it’s not always a problem inside the box making the heat; the problem you see may be the beginning of the story. As an industry, we need to look at these systems to provide the reliability and efficiency our customers expect. This is going to become increasingly important as energy costs rise, so be sure to stay at the top of your game. l

Cody Mack has nearly 20 years’ experience as an installation contractor, service technician, application engineer and, most recently, as training manager for Caleffi North America. He’s a family man, gear-head, and motorcycle enthusiast with a common-sense approach to hydronics. Cody can be reached at cody.mack@caleffi.com.