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Performing Critical Hydronic Maintenance

June 3, 2014
Modulating condensing boilers and the hydronic-system components that interact with them require care for peak performance to be maintained.

In the past, facilities engineers and building owners—even those who typically were attentive to HVAC maintenance—were willing to “let the boiler slide” for months or even years without a proper checkup. This happened because early generations of atmospheric gas boilers were designed to operate for long periods without maintenance.

Today, the national boiler codes specify that all commercial boilers be inspected by a licensed boiler contractor at least once a year. That is 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 a year. Modulating condensing boilers and the hydronic-system components that interact with them require care for peak performance to be maintained.

Record Keeping Is Essential

An essential part of a boiler-maintenance process is a maintenance plan. The trail of information often is neglected, lengthening the time needed to perform system diagnostics. As a boiler-maintenance specialist, you should keep a detailed record of all boiler-room conditions and all of the work you perform on a boiler. Basic record keeping is essential.

Keep in mind that many boiler problems stem from mistakes made during installation, so begin your boiler maintenance by assessing the overall picture. Look closely and record in the maintenance log what you see regarding system piping, venting, gas or oil supply, and conditions in the mechanical room.

A boiler start-up sheet should be used to evaluate system performance and spot trends that affect a boiler’s operating pressure (for a steam boiler), operating temperature (for hot-water systems), stack temperature, and water-level controls.

A start-up sheet not only records the basic situation as you see it today, it sets a baseline for later maintenance and service calls—whether they are routine or generated by a no-heat call.

Key Maintenance Categories

Key categories for routine maintenance include venting, combustion air, gas or oil supply and/or filtration, water quality and piping, electrical wiring, diagnostics, and controls. Let’s take a look at each of these.

Venting. Check all Category I venting (non-condensing, negative pressure) for a white chalky substance on the outside of the vent.  This substance often indicates condensation inside the flue. If signs of condensation are present, verify the boiler is piped properly and operating at the prescribed temperature. If the vent material shows signs of condensation, it may be necessary to check the flue or the boiler for damage.

Category III and IV positive-pressure-vent-system appliances require sealed venting with stainless steel or specific plastic vent material to withstand the corrosive effects of condensation. Installers and service professionals need to ensure the correct material is used. Check appliances during every annual maintenance procedure to ensure their seal is tight.

Combustion air. For atmospheric systems, check for any blockage of combustion-air openings. Check the free flow of air into atmospherically fired boiler rooms at least every six months. For ducted combustion units, check for blockages routinely. Also, clean and check the system’s filters at least once a year; every six months is even better.

Gas or oil supply piping and filtration. Check gas pressures while the system is at peak load to determine if there is a measurable reduction during peak operation. This helps to answer any questions about a boiler’s ability to meet heat demand and the quality of combustion.

Problems with gas-line pressure can be a real nuisance in certain parts of the country. Areas that rely on older gas lines may not be able to supply sufficient pressure during peak demand.

Inadequate gas pressure can cause rough light-off and lock-outs. Also, it often is misdiagnosed as faulty ignitors, ignition controls, or gas valves. Proper sizing of gas piping between boiler and gas meter should be confirmed before inadequate gas pressure is assumed.

Typical gas pressure required by older commercial boilers is 4-plus in. w.c.

If there is any doubt about the available pressure, you may need to put in a call to the gas company to see if the line pressure can be increased.

Clean or replace fuel-line filters on oil boilers at least once a year or, if the tanks are older and likely to contain sediment or sludge, every six months. When possible, take a boiler off line for a few hours during and after fuel delivery.

Water quality and piping. Any corrosive activity on piping should be addressed immediately, as it could be evidence of air infiltration. All visible piping should be checked for signs of deterioration during each scheduled maintenance visit. Check the boiler’s relief valve to ensure it is not leaking, and ensure there is proper pressure in the system.

Many newer boiler designs use stainless steel or aluminum in their heat exchangers. The manufacturer may have requirements for water quality (pH, hardness, etc.). Be sure you know what these requirements are, and test for them when inspecting a boiler.

Electrical wiring, diagnostics, and controls. Check all wiring in the system for overheating. Hardening or melting of insulation certainly will cause problems. Among other things, it can incapacitate or otherwise influence diagnostic systems, disabling safety (boiler-off) checks that would turn off the boiler in the event of problems.

Check to be sure the boiler shuts down on high limit and at low water cutoff. Check operation of the aquastat to be sure the boiler shuts down at the set-point temperature.

Check the flow switch to ensure the boiler shuts off under no-flow conditions. Also, be sure to test the igniter for ohm resistance or the micro amp signal (depending on type) to ensure readings are within acceptable guidelines.

A Long and Harmonious Life

Boiler maintenance and service always should be made in accordance with the manufacturer’s recommendations. Most boilers are unique and designed to perform for a specific application. But whatever the boiler’s application, the key to preventing maintenance problems includes careful and deliberate start-up 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 customers.

Greg Jannone is president of William Jannone & Son Inc. He can be reached at 732-469-0582. Nate Warren, hydronic sales manager, Bradford White, and Joan Mishou, customer-service manager, Laars Heating Systems Co., contributed to this article.

SIDEBAR: A Four-Pronged Approach to Mod-Con Maintenance

Using a four-prong approach can assist maintenance personnel in keeping up with the required maintenance on modulating-condensing boilers, according to Mike Haigh,
government/contractor sales manager for Federal Corp., an Oklahoma City-based manufacturer’s rep firm.

“First, boilers must be inspected routinely—every few months isn’t overkill,” Haigh said. “They will not necessarily require maintenance at each inspection, but it is good to know when they will before an issue expands. At the top of this list is boiler refractory. Some modulating-condensing designs have very small combustion chambers in which the refractory takes a beating. The material may need to be replaced more often than expected; when deterioration is apparent through the sight glass, it’s time to replace it. If refractory deterioration is not addressed promptly, it is possible to damage the heat exchanger beyond repair.”

No. 2 on Haigh’s list: igniters. Modulating-condensing boilers can operate with wet combustion chambers and, thus, are susceptible to moisture damage. Oxidation on the flame rod/igniter can cause nuisance shutdowns. Over time, the flame rod can fatigue because of heat/cool cycles, and the gap between the igniter and flame rod can change. If this gap gets too wide, there can be nuisance lockouts or rough lightoffs. Haigh recommends changing the igniter at least once a year.

Above: an example of “coffee grounds” that have formed inside of a boiler’s combustion chamber. Below: the same combustion chamber after a thorough cleaning. Photographs courtesy of Mike Haigh.
Fireside cleaning is next. In modulating-condensing boilers, water vapor can mix with impurities in the air and fuel to form “coffee grounds” inside the combustion chamber. These must be removed, lest they impede drainage of boiler condensate. If the combustion chamber does not drain properly, the refractory can become soggy and deteriorate prematurely. Heating surfaces need to be cleaned annually to keep the efficiency as high as possible. Remember: Scale the thickness of an eggshell can reduce efficiency by 10 percent or more.

Lastly, proper drainage is essential.

“Even something as mundane as drainage can’t be ignored with modulating-condensing boilers,” Haigh said. “Condensate can have a very acidic ph level as low as two or two-and-a-half. It needs to be drained out and neutralized.

“Modulating-condensing systems are amazing in their ability to produce heat efficiently,” Haig added, “but they must be maintained.”

SIDEBAR: Advanced Controls Aid Maintenance Personnel

As with most HVAC equipment, boilers are seeing an influx of sophisticated control systems.

“Our task of moving heat from the combustion chamber is much the same today as it was decades ago, albeit with far greater efficiency,” Bill Root, general manager, Laars Heating Systems, said. “Where we’re seeing the greatest influence of new technology is in boiler control systems.”

In addition to enhancing boiler efficiency, advanced controls can have a positive effect on boiler maintenance and operation.

“Boilers will become easier to troubleshoot and maintain because of advanced electronics, more user-friendly displays and ‘language,’ and modular component design,” Root said. “In the near future, advanced electronics will likely migrate towards boiler self-diagnostics that will indicate not only what may be wrong in the boiler system, but what steps should be taken to fix it.”