Boiler Operation and Maintenance: Save Fuel, Prevent Damage and Avoid Accidents
Each year, hundreds of accidents are reported involving steam and hot-water heating boilers in schools, businesses, public buildings and other facilities. Most of these incidents are attributed to malfunctioning low-water cutoffs, poor maintenance, operator error or corrosion. Regular maintenance and testing of control and safety devices are essential for any boiler.
Some of these boiler control and safety devices are discussed below, with recommendations for testing and maintenance. Consult with your boiler manufacturer, contractor, insurer or state authorities with any questions about more detailed procedures and requirements.
Maintaining Boiler Safety Relief Valves
The purpose of the safety relief valve is to provide security and protect boilers from exceeding their limits by relieving all the pressure inside. Every steam and hot-water heating boiler needs at least one safety or safety relief valve of sufficient relieving capacity to meet or exceed the maximum burner output.
Safety relief valve performance can be affected by several things, such as internal corrosion or restricted flow, which can prevent the valve from functioning properly. Internal corrosion can cause "freezing", or binding of safety and safety relief valves, which is generally caused by slight leaking or "simmering" due to improper seating of the valve disk. If observed, this condition should be immediately corrected.
To assure that a valve's mechanism will operate properly:
- The try-lever should be lifted once a month and the valve set pressure should be tested annually
- The valve must be set to open at or below the maximum allowable working pressure established by the manufacturer, which is listed on the boiler nameplate or stamping
- If a valve will not operate or does not reseat properly when tested, the boiler must be shut down immediately and the valve repaired or replaced
- Do not operate a boiler too close to the valve setting because it will cause valves to leak slightly, resulting in an internal corrosion buildup
The same conditions that make other safety devices malfunction can also affect the safety relief valve. Regular maintenance and testing are essential.
Boiler Water Level Control and Low-Water Fuel Cutoffs
These devices provide a water-level control function and a safety feature of a low-water fuel cutoff device. Steam and hot-water boilers should always have two such devices (a primary and a secondary low-water fuel cutoff) and many jurisdictions require two on steam boilers. Attach the devices to the boiler through separate openings to prevent a restriction in the connecting piping from disabling both devices.
When installing and maintaining piping, it is important to remember:
- Always keep piping open and free of scale or sludge buildup
- Use "cross tees" so piping can be easily cleaned and inspected
- Connection issues can be observed when flushing out or draining the float chamber of the low-water fuel cutoff
- The water level should quickly return to normal in the gauge glass when the drain valve is closed; a slow return is an indication that the connecting piping to the boiler is restricted
The most common water-level control and low-water fuel cutoff devices consist of two main components: a float chamber and an electrical switch operated by a float in the float chamber. A malfunction in either will prevent the cutoff device from operating.
Malfunctions in the float chamber are generally the result of neglect. Tampering and age most often cause failures in the switch and associated wiring.
As the water level in the boiler drops, there is a corresponding drop in the float. When the float reaches a preset position, it activates an electrical switch that shuts off the burner. Sludge and sediment accumulate in the bottom of the float chamber.
Failure to regularly flush out the float chamber will cause the sludge to build up, preventing the float from dropping down to the shutoff level. Note that flushing the float chamber should not be considered as a test of the low-water cutoff.
Flushing and Testing Low-Water Fuel Cutoffs
When the boiler is operating, low-water fuel cutoffs should be flushed and tested periodically to ensure proper operation. The float chamber on the low-water fuel cutoff should be thoroughly flushed to remove any accumulated sediment.
Since flushing and testing may require lowering the boiler water to the minimum safe operating level, qualified personnel should use extreme caution.
- Never allow the water level to drop out of sight in the water gauge glass
- Low-water fuel cutoffs should be flushed daily for steam boilers operating at more than 15 psig and weekly for those operating at less than 15 psig
- Be sure the burner stops when the water level drops. If it does not or the water level does not quickly return to normal, shut down the boiler and correct any problems
In addition to flushing the low-water fuel cutoffs, a slow drain test should be done. For all steam boilers, this should be done annually. For hot-water boilers, the slow drain test should be done annually but only if this can be done without draining the entire system and without draining a large quantity of water from the boiler.
Disassemble, clean and check low-water fuel cutoff devices at least once a year. An ideal time to conduct the slow drain test is immediately after this annual maintenance. Unless you are very familiar with the process, have an experienced technician perform this type of maintenance.
The electrical switches and wiring are generally reliable and do not require a lot of maintenance.
- At least once a year, clean the switches and remove any dust or dirt
- The covers should be kept tightly in place except when open for cleaning
- During the annual cleaning, examine the wiring for signs that insulation is cracking
- Keep all connections tight
It is not unusual for a maintenance worker to remove the cover and install a "jumper" wire to prevent the switch from operating. This starts out as a temporary convenience, often to "fix" a boiler that keeps shutting off on low- water while being operated at high demand or as a temporary means to test other circuits in the control system.
This bypass can easily become permanent and dangerous. A boiler that regularly shuts down indicates a very serious problem that could lead to an accident. A jumper wire should never be permanently installed in a low-water device and only a qualified technician should use a jumper to test another circuit.
Maintaining and Protecting the Boiler Fuel System
The fuel system, particularly the burner, requires periodic cleaning and routine maintenance. Failure to maintain the equipment in good working order could result in higher fuel costs, the loss of heat transfer or even a furnace explosion.
Modern fuel systems are very complex, consisting of both electronic and mechanical components. Over time, issues can arise:
- Ignition transformers deteriorate or fail
- Ignition electrodes burn and become coated
- Fuel strainer and burner equipment clog
- Fuel valves get dirty and leak
- Air/fuel ratios drift out of adjustment
- Flame scanners become dirty
Many users contract with their gas company or oil service company to periodically check and maintain their burner equipment.
Properly maintained equipment should be safe and reliable, but devices installed to assure safe operation are sometimes viewed as an inconvenience. The personnel who operate the boiler may tamper with or adjust these devices, thereby compromising safe operation of the boiler.
The safety feature most often adjusted is the burner purge cycle, designed to prevent furnace explosions caused by a buildup of unburned fuel in the furnace chamber. The cycle length is determined by the equipment manufacturer to purge fuel from a leaking fuel valve or an unsuccessful ignition sequence.
You may be tempted to shorten or even bypass the cycle. Don’t! Doing so greatly increases the chances of a serious explosion.
Keeping the Water Gauge Glass Clean
The water gauge glass, or sight glass, on a steam boiler allows the operator to visually observe and verify the actual water level in the boiler. If not properly cleaned and maintained, a gauge glass can seem to show there is enough water, when the boiler is actually operating in a low-water condition.
A stain or coating can develop on the inside of glass where it is in contact with boiling water. After a time, this stain gives the appearance of water in the boiler, especially when the glass is completely full or empty of water.
Another indirect cause of accidents is clogged connection lines to the gauge. In that case, the gauge glass may show normal water levels while in fact the water level may be low. The piping connecting the gauge glass to the boiler should be cleaned and inspected regularly to assure it remains clear.
Often, a boiler is operated with the isolation valves to the gauge glass closed because the glass has been broken or is leaking. Replace the glass, even if the boiler must be shut down, because a lot of damage can occur from operating a boiler without a gauge glass. Some operators routinely replace the glass and seals during annual maintenance because it is so important to verify the actual water level.
The Purpose of the Boiler Stack Temperature Gauge
A stack temperature gauge is normally installed on a boiler to indicate the temperature of the flue gas leaving the boiler. A high stack temperature can be an indication of boiler tubes fouling with scale and/or soot. The stack temperature can also be impacted by a deteriorated or burned baffling inside the boiler (which allows gases to bypass heat transfer surfaces in the boiler), or an out-of-adjustment burner.
These conditions generally develop slowly over a long period of time, so the person who operates the boiler can become accustomed to the gradually rising temperature. Approximately 1 percent in boiler thermal efficiency is lost for a 40-degree F increase in stack temperature.
Prevent Accidents by Using a Boiler Log
Most boiler accidents can be prevented. Boiler operating and maintenance logs are the best method to assure a boiler is receiving the required attention and to provide a continuous record of the boiler's operation, maintenance and testing. Because a boiler's operating conditions change slowly over time, a log is the best way to detect significant changes that may otherwise go unnoticed.
To keep a boiler in good operating condition, boiler personnel must be responsible for its operation and maintenance. Maintenance and testing should be performed and recorded in the log on a regularly scheduled basis. The responsible individual should initial the log to verify each operation performed, who performed it and when it was done.
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Disclaimer: This material is designed and intended for general information purposes only, and is not intended, nor shall be construed or relied upon, as specific legal advice.
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