Even trade professionals who are very attentive to HVAC maintenance can be willing to "let the boiler slide" for months or even years without a proper checkup. Why? In many cases – especially with early generations of atmospheric gas boilers – this happened because the equipment was designed to go a long time without maintenance.
Today, the National Boiler Codes specify that all commercial boilers must be checked by a licensed boiler contractor at least once each year. That's a good start, but the truth is that as the market has pushed the need for higher efficiency equipment — such as condensing, fully-modulating systems — boilers and burners may require two or more maintenance checks each year. Here are some insights to help you on the commercial boiler maintenance call.
Before we even start with the boiler maintenance process, make sure that as you put a maintenance plan in place you carefully record baseline conditions. Keep a detailed record of all conditions and the work you do. The trail of information is too often neglected, lengthening the time it take to perform system diagnostics. Basic record-keeping is essential.
The Burner is the Gateway
At every step on a boiler service call, make sure all the electrical connections you come across are secure. Check all wiring for overheating. Hardening or melting of wiring or connections is a sign of a more serious problem, such as chambers firing too hot.
The first thing to do on a routine inspection of the burner in a modulating-condensing boiler is to remove the burner itself. This will allow you access to inspect the combustion chamber and the coils inside.
Check the flue passages. These will tell you if the boiler is burning properly. If there's soot in the flue passage, the system may be running rich or have insufficient combustion air. If there's moisture in the vent pipe, the system is running too cool.
Inspect the vent pipe, looking for any white, powdery residue that may be left behind from condensation taking place in the vent. Condensate is extremely acidic and can eat through the vent pipe material. Be sure to maintain stack temperatures above manufacturer minimums to prevent this.
Check all flame-sensing rods. Also, examine the spark rods to ensure they're properly gapped. Always check the ceramic retainer that holds each of these to be sure there are no hairline fractures.
Beyond the Burner
Outside the burner chamber, check fans and blowers for buildup of dirt on the fins. If the boiler is equipped with filters on the make-up air, clean or replace them.
The burner can be enabled during your inspection, but the gas cock should remain closed to prevent the main burner from firing. Inspect all safeties and interlocks. Always keep in mind that testing should mimic unsafe conditions, not create them. First on the list are the low and high gas pressure safeties. For the low pressure safety, simply remove the gas pressure. For the high pressure side, set the safety's setpoint below what the current gas pressure is. If the circuit opens, they’re working properly.
Next, check the block valve(s). If the unit is equipped with double block-and-bleed valves, the bleed valve will need to be held shut in order to check the block valves.
Screw a fitting with a hose attached into the port of the block valve, and place the end of the hose into a cup or bottle of water. If the hose produces bubbles, the block valve leaks and is in need of replacement.
Next, inspect combustion air proving switches. Simply remove the air lines to make sure that the switches will open. Test the purge timer. If the boiler has an adjustable purge timer, be sure that it's at the factory setting.
While checking all of the safeties and controls, be aware of the time it takes to light the boiler after each shut-off. Some boilers and controls require more time because of the post- and pre-purge and ignition timing.
With an atmospheric burner, it may be appropriate to allow the pilot to light, but not to fire the main burners. Check the pilot flame and compare the inlet gas pressure to the factory recommendations.
Examine the Flue Gasses
With the burner running, and after the boiler reaches full operating temperature, take a close look at the flue gasses and make sure the temperature is correct.
Monitor oxygen, carbon monoxide, and carbon dioxide levels present in the flue with a combustion analyzer during and after the warm-up period. Typically, you're looking for eight to 10% carbon dioxide, and preferably less than 20 parts per million carbon monoxide. This process must be monitored from the low fire all the way through to high fire settings.
Because you can't see the flame, a combustion analyzer is the only way to properly test and adjust sealed combustion boilers. An improperly adjusted burner will cause units to run dirty, fouling combustion chambers.
To alter temperatures in the flue, and the gasses present, the combustion air and modulating fuel valve must be adjusted. Controlling the precise rate of fuel and oxygen being burned, and the temperature of the boiler determines whether or not the boiler burns cleanly and efficiently.
When the boiler is warm, check the operator, and the high temperature limit. To do this, fire the boiler at its highest rate, forcing it to exceed setpoint temperatures of both the operator and the high limit. Both must have the ability to interrupt the burner when tripped.
A Long and Harmonious Life
Most boilers are unique and are designed to perform for a specific application. Maintenance and service should always be made in accordance with manufacturer's recommendations.
Whatever the boiler's application, the key to preventing maintenance problems starts with a careful and deliberate startup of the equipment, routine monitoring and logging, and six-month scheduled maintenance visits to promptly address little problems before they gain weight.
The result will be a long and harmonious life for the boilers you service, as well as harmony between you and your boiler customers.
Jim Docter is the senior service technician Seaman's Air Conditioning & Refrigeration, Inc, Grand Rapids, MI. Docter has 22 years of HVACR industry experience and has attended numerous service schools and specialized controls training courses. He can be reached at 616/458-1544, or by e-mail at email@example.com.
Mark Hughes is the U.S. national service manager for Rochester, NH-based Laars Heating Systems Company. Hughes has 35 years experience in the plumbing, heating and HVAC industry, including 15 years with Laars in applications training and service. He can be reached at 603/335-6300, or by email at MHughes@laars.com.
Ed.Note: In all photos, Seaman's Senior Technician David Henney visited a customer's multiple Laars boiler installation to perform annually-required State of Michigan CSD-1 testing of all the boilers' safety devices. This is part of the firm's routine maintenance schedule each fall.