Cleaning up the ‘Cons

By Bob "Hot Rod" Rohr

Radiant Expert

Modulating condensing boilers and heaters (also known as mod-cons) are appearing everywhere these days. Many of the leading boiler manufacturers offer at least one model. More brands and sizes are in the works for release this fall.

For the radiant contractor, mod-cons are as close to perfect as one could ask for in a heating appliance. They love to operate at low-fluid temperature conditions. They condense when the return temperatures fall below the fuel dew point. A secondary heat exchanger captures the energy from the condensate before the byproducts of combustion continue out the flue.

The modulating feature allows the unit to adjust its output to better accommodate a varying load. Most have microprocessor controls and other cool features such as domestic hot water priority, outdoor reset, data logging, set back and boost programs. That's a nice bag-of-tricks for the installer.

Most will do some self diagnostics as well. Some indicate an error code, while others will actually spell out the error location. Various brands allow you to plug in your laptop and look at fault history and read various outputs, both temperature and flame rectification signal. Lochinvar's Knight will scan this data and communicate it to your PDA via an infrared signal.

What's not to like? You can choose a brand based on features that best fit your application. Some are wall mounts, some floor, and a few provide both wall brackets and adjustable feet for leveling in the floor mount position. Some brands use a coiled stainless HX, other use cast aluminum alloys.

When it comes to cleaning, mod-cons are a bit needier than the old gas fired cast iron blocks. Yearly maintenance is a must, and may be a warranty requirement. A more frequent cleaning may be needed if the mod-con lives in a dirty environment.

Water quality is an issue. A thin coating of scale or sediment may cause the heat exchangers to overheat and lose performance, or worse, cause them to fail prematurely. (Think copper fin boilers.)

Clean fill fluids and proper circulator sizing need to be addressed. I like to run a hydronic cleaner and conditioner through the system first. The installation manuals may provide you with a list of product names to use. I have been happy with the www.rhomarwater.com products. These were blended specifically for a safe cleaning of today's multimetal systems.

Be sure the fill water meets the criteria listed in the installation manual. It may be necessary to bring fill water to the job, if the on-site water is out of spec. Also, consider an approved hydronic system treatment chemical. Hydronic conditioners are designed to scavenge O2, balance pH, and provide a very thin protective film on the metal components to reduce or prevent corrosion. This is a simple way to protect your customer's investment.

With glycol-ed systems, ensure that the brand you use is compatible with the boiler materials. This is especially critical with aluminum heat exchangers.

The fireside of the heat exchanger also needs attention. Some of the systems I have installed seem to need more frequent attention than others because they are subject to dirty, dusty air. The heat exchanger pictured in the photo is in a feed store surrounded by a gravel parking lot and farm fields. Even with the intake air 15-ft. above the parking lot, I suspect this unit pulls a lot of dust. I've noticed one condenser brand now includes an intake air filter. An intake air filter would be an excellent addition to a dirty environment installation. Keep in mind, with this filter, you just moved the maintenance item upstream and the filter will need to be maintained. Install it in such a way that it is easily removed for cleaning or replacement.

Another tip: Inspect the heat exchangers with a camera. I've found the Rigid See Snake Micro easily fits into the intake and exhaust connections to "look" at the conditions inside. It is the only way I have found to view the rear heat exchanger located behind the target wall.

The See Snake Micro also fits into the fan intake so that you can check those conditions. I found one blower with a very thick layer of sheetrock and construction dust. This particular mod-con pulled outside air into the case and then into the fan. But the boiler case leaked badly and it sucked in a lot of the construction dust from the tile cutting and sheetrock installation. Also, the end of the day site sweep-up throws lots of dirt and dust into the air. You may have to clean the mod-con shortly after installation, depending on construction site conditions.

Consult with the heater manufacturer regarding cleaning products. Some allow a de-lime type of cleaner to be used followed by a good clean water flushing. I have located some soft plastic brushes at an equine supply company. They clean between the heat exchanger coils without scratching them. Stay away from steel wire brushes, as you would when cleaning a stainless wood stove flue pipe.

I've assembled an array of breakdown tools to fit the various brands I install. The fasteners are typically metrics, and small Torx headed bolts, so plan accordingly.

I also practiced breakdown procedures, on various brands in my shop, in preparation for inevitable cleanings.

Always recheck the adjustments after you reassemble them with your combustion analyzer and leave a dated copy of the printout in the job folder or inside the unit. Also check all the wiring connections. A weak or corroded connection will throw fault codes until the cows come home. I also check the brand-new installs for loose wiring connections and harnesses when I install them. The stagecoach ride to Rogersville often jars components loose.

Hope this helps! Reach me at www.showmeradiant.com with questions, concerns and ideas.

Bob "Hot Rod" Rohr is particularly interested in hybrid radiant systems -- systems that utilize solar and wood energy in addition to, or in place of, fossil fuel. Also, systems that incorporate different methods of heat delivery. He owns and operates Show Me Radiant Heat and Solar, Inc. in southwest Missouri. Reach hot rod at hotrodradiant@aol.com or by phone at (417) 753-3998.