When I say the Mod Squad, I’m not talking about the diverse trio of undercover police agents that gave television a breath of fresh air in the late-1960s and early-1970s. No, this is about so much more than the redemption of Pete, Julie and Linc’s past.

I’m talking about The Mod Con Squad, the technicians whose responsibility it is to make sure the modulating condensing boilers are commissioned and serviced properly.

When you’re in the mod con boiler business, you need to take your technical acumen to the next level or you won’t be in the industry for long.

I can’t tell you how many times someone has told me they’ve had their boiler serviced every year since it was installed five years ago but, as of late, they're starting to have problems with it. Invariably, as soon as I pop the panels and access the heat exchanger, it becomes clear as a brand-new sight glass that it’s never been serviced properly. 

Don’t be a ripping-and-running service tech like those guys. They’re a dime a dozen. Differentiate yourself! Do it as if you want to be the best. Go big or go home.

Be prepared 

Before I begin working on these boilers, there are a few things I prefer to have in order first. Be prepared is not just the Boy Scout motto — it’s a great way to start any service/maintenance process.

I like to have a copy of the installation and service manuals with me for that specific boiler. It can be a hard copy or a document you’ve saved on your phone or iPad. A Weil-McLain Ultra Series 3 isn’t the same as a Lochinvar KHN, which is different from a Lochinvar KBN. 

Make sure you have the right tools and test instruments with you. Here are some of the things I make sure are represented in my tool bag: a can of compressed air, clean cloths, grit cloth, a NIOSH respirator mask, OEM replacement burner gaskets, metric and standard ball-end Allen wrenches, metric and standard nut drivers, metric and standard gear wrenches, magnetic tray, TDS strips, pH strips, multi-meter, soft brush, flashlight and inspection mirror. I like to wear a headlamp as well; having the light follow your head movement makes too much sense not to.

Other obvious tools that won’t fit in your tool bag are a small shop vac and a properly calibrated combustion analyzer with a printer. 

Step by step

Ready to dig in? Cool! Me too!

Check the boiler fault history: The reason for this is simple. If something is amiss with this piece of equipment, you’re going to want to know about it before you pick up a tool.

The manufacturers give us this tool to be used to our advantage. Use it. Take a snapshot of the screen with your phone; the more you document, the better.

Access and clean the heat exchanger: There’s some work involved here and the first time on any specific boiler is going to be a lesson you can’t learn any other way except getting your paws dirty. Don’t let that stop you. Once you do it, the second time will be infinitely easier. 

You’re likely going to be removing the combustion blower, gas valve, cover plates, sight glasses, igniter and sensor, each with a gasket that will want to rip to shreds the second you touch it. Go slow and easy removing each one.

During this process, the magnetic tray will be your best friend. Most of those screws you’ll be removing won’t be something you’re going to have on your truck. Lose one and your day just went from promising to an anxiety-ridden search.

For the cleaning process, refer to the manufacturer’s instructions, which tend to be very specific on how to proceed. We don’t want manufacturers voiding heat exchanger warranties because we did this when they asked for that. Follow the manual; it’s why you have it.

That said, I’ve used CLR, a Scotch Brite pad and a damp cloth with good results. Then I flush it with water until the water coming out of the drain is clear.

 Clean the burner, if applicable: Be careful here. You don’t want to damage it and you don’t want it hurting you. This is where your mask becomes your MVP of tools. Wear it and maybe some nitrile gloves. Some of the ceramic fibers may be carcinogenic when overheated. Don’t take the chance and, again, follow the manufacturer’s recommendations.

Clean the flame sensor: It needs to be clean and it won’t be when you get to the jobsite, I guarantee it. I typically use light steel wool to shine it up. I also inspect the ceramic part of it to make sure there aren’t any hairline cracks. If there are, do your customer and yourself a favor by replacing the sensor. It’s part of why we’re there — to prevent future problems.

Clean electrodes and check gap: Use the same procedure here as the flame sensor for cleaning; and check the manufacturer’s suggested gap, usually 1/8 inch.

Inspect HX gaskets: The gaskets need to be intact. If they aren’t, the combustion process will not perform as intended. It’s why I keep a bunch on hand. They’re inexpensive, but become very expensive if you have to make a run to the supply house in bad weather and rush-hour traffic. We’ve all got decent-sized work trucks. Let’s make sure we're stocking them with the little things that don’t take up much space and usually aren’t readily available. I’d bet I replaced a gasket on every third mod con, at a minimum.

Perform combustion analysis and adjust gas valve, if necessary, to meet manufacturer’s specifications: This is where things get real. As real as Linc, Julie and Pete avoiding jail time for the indiscretions of their youth.

It’s essential to do a combustion analysis on every startup and on every annual maintenance call. Start with a quality, properly calibrated combustion analyzer with a printer. You’ll want to leave documented results of your analysis so the next technician has a historical record of the burner’s performance. It’s also reassurance for your customer that you’ve done your due diligence.

The burner should be checked at both low fire and high fire after running for at least 15 minutes; a steady state is what the engineers call it.

Most boiler manufacturers provide a test port for your analyzer probe. But if there isn’t one, you’ll have to make one. I drill a 1/4-inch hole, run a pipe tap through it and use a stainless-steel plug when I’m done. Using a piece of tape is unprofessional in my opinion and potentially unsafe. Erring on the side of caution is the best option.

Now anyone can turn on an analyzer, insert a probe into the flue pipe and press print after a few minutes. It’s what you see in those results that can separate you from the pack. Is it burning lean? Burning rich? Can you tell, either way, by looking at the CO₂ or the O₂? How does the excess air look? Is the amount of CO produced within an acceptable limit? Flue gas temperature where it should be?

The results should fall within the range set forth by the manufacturer. I wouldn’t know those unless I opened and read the manuals. I even use a highlighter. I am a heating geek to the nth degree. I love digging in and reading the stuff most techs don’t think they need or have the time for. They’re wrong on both counts.

Oxygen and carbon dioxide are inversely proportional to one another. What the heck does that mean? If the O₂ is high, the CO₂ is going to be low. And if the O₂ is low, the CO₂ is going to high. If the O₂ is somewhere in the middle, CO₂ will be lurking in the same neighborhood.

If O₂ is high, you’re burning lean. You have too little gas (underfired) or too much air. If O₂ is low, you’re burning rich. You have too much gas (overfired) or too little air. If your excess air is too high, your efficiency is going to suffer.

If your CO is high, a lot more than efficiency is going to suffer.

Don’t underestimate the number of resources available to you for further combustion analysis knowledge. I encourage you to engage in them. Try YouTube first. Tru-Tech Tools has many great videos using Bacharach, Testo and other analyzers — step-by-step stuff that won’t leave any questions unanswered.

Ray Wohlfarth has spent much of his life in boiler rooms and his books won’t let you down. Much of the content deals with CO, CO₂, O₂, excess air, combustion efficiency, CO-free air and flue gas temperatures. My favorite is “Lessons Learned Servicing Boilers.”

Heatinghelp.com’s “The Wall” will have all kinds of information on combustion analysis shared by some of the brightest people in our industry. Just type what you need in the search box and wait for the fields to populate. Jim Davis may be the foremost authority on the subject, and he hangs out there regularly.

And don’t overlook the obvious; analyzer manufacturers’ websites have excellent videos and PDFs you can download for future reference.

Adjust control parameters to fit the type of system better, if necessary: When setting up the control parameters, you must have, at least, a basic understanding of the system the boiler is serving, its occupants and your local weather.

Is it a high-temperature system? Cast-iron radiators, cast-iron baseboard, fin-tube baseboard and fan coils would fit this category.

Is it a low-temperature system? Radiant floors, walls or ceilings are the culprits here. High mass or low mass? Can it recover from setback temperatures?

Setting the outside reset numbers is, for the most part, straightforward. You’ll need to know what the outdoor air low temperature will be, the corresponding supply water temperature you’ll want to go along with it, the outdoor high air temperature that your boiler will still be operating at and its corresponding supply water temperature.

For my area, Chicago, my numbers using a low-temperature system would look similar to this, with the outdoor air temperatures based on the Manual J heat loss load calculation:

• Outdoor low air temperature: 4 degrees

• Setpoint at low air temperature: 120 degrees 

• Outdoor high air temperature: 65 degrees

• Setpoint at high water temperature: 80 degrees

These numbers set the outdoor air reset curve.

The tricky part is figuring out how aggressive you want to be with the numbers. Do you set it for optimal efficiency using it at 65 degrees to 70 degrees indoor air temperature? It works for me, but it’s not up to me. It’s up to those inhabiting the space and each one of those creatures has a different creature comfort zone.

There are plenty of other control settings to investigate such as cascading multiple boilers, ramping, boosting, the use of a domestic hot water indirect tank, offsets, differentials, warm weather shutdown temperatures and pump exercising. Not all boiler controls are created equal. Do your homework.

Flush the condensate line: Easy enough, right? Use an acid neutralizer kit. The condensate from these boilers is acidic and you don’t want it attacking your plumbing pipes. Not to mention the fact it’s required by code in most areas.

Check static and dynamic gas pressure: This is critical. Please don’t even attempt doing a combustion analysis without first checking gas pressure while the boiler is idle (static gas pressure) and while it’s operating (dynamic gas pressure). It should be, here’s that phrase again, within the manufacturer’s specifications.

Check voltage polarity and system ground: If your hot and neutral are crossed, you’re going to have flame rectification problems. If you have a poor ground, the flame rectification circuit will be marginalized. Correct as needed.

Check boiler piping to verify it meets manufacturer’s specifications: This is important, as well. With only a few exceptions, modulating condensing boilers hold very little water; two to three gallons at best. For that reason alone, I recommend using a low-water cut-off on every mod con boiler. It’s not an inexpensive investment. It only makes sense to protect it as best as possible.

Boilers with water-tube heat exchangers are highly restrictive; fire-tube heat exchangers are more forgiving. For these reasons, make sure you pipe them correctly, ensuring proper flow through the heat exchanger. Its life depends on it. The mod cons with water tubes must be piped in some variation of primary/secondary piping, whether it be closely spaced tees, a hydraulic separator or a buffer tank.

If you’re not entirely sure on the details of primary/secondary piping, do whatever it takes to make sure you are. Start with a piping schematic. Don’t make it up as you go along. That approach rarely ends well.

And unless you’re really polished on designing hydronic piping systems, I’d recommend the same thing for boilers with fire-tube heat exchangers — unless they have a high water content. I can only think of two; one manufactured by HTP and the other by Viessmann.

Check system water quality: Would you knowingly pump contaminated gasoline into that tricked-out work truck of yours? No. Who would? Then let’s not put contaminated water in our high-end hydronic systems because you’re going to get the same result; machinery that won’t perform as the manufacturer intended. 

We didn’t pay too much attention to this in the past but with today’s high-end equipment, boiler water chemistry is more important than ever. Hardness, pH balance, TDS and chlorine play a crucial role in the lifespan of the heat exchangers. The boiler manufacturers will provide some ranges you’ll need to be within.

Clean your piping systems before connecting them to the new boiler and add conditioner after the new boiler is installed. 

For additional information, check out Caleffi’s idronics “No. 18, Water Quality.” 

Don’t forget the usual tasks associated with a boiler clean and tune; check for gas leaks, flue pipe pitch and integrity, health and safety issues, pump maintenance, tank pressure check and adjustment, clean y-strainer, flue draft, water leaks, etc.

Your brains, eyes and ears are your best troubleshooting tools. Keep them open and your job will be easier.

The Mod Con Squad 

They were young people in trouble with the law.

Pete, who was wealthy, stole a car. Linc got arrested during the infamous Watts riots. Julie ran away from her troubled past. Everything they did in their past was done with felonious intent. But they redeemed themselves. They completely reinvented their game.

We’ve got to be reinventing and improving our game, too. More than ever, we need to raise the bar in our trade to continue its growth and attract young technicians. If we don’t, who or what is going to replace us?

I can’t speak for anyone else but when it comes to our trade, if I don’t know something or don’t know how to do something, it bothers me to no end. It bothers me enough that I do something about it. I’ll go to seminars, take classes, watch videos, read a book or a technical manual with all the zeal of an OCD action figure. 

How about you? Are you ready to become part of the elite? Part of the Mod Con Squad? Yes?

Let’s go to work.