Boiler Inspections

Boilers are inspected annually to ensure they are safe to operate. The inspector checks safety controls to make sure they work properly and inspects inside the boiler, both the waterside and fireside.

The inspector looks for signs of problems that should be investigated, such as:

  • Overheating
  • Excessive scale
  • Corrosion
  • Deformed or damaged pressure vessel components

Before the inspector arrives, you can take the following steps to ensure the boiler passes the inspection:

  1. Perform an operational check of the boiler’s interlock controls. Required controls vary with fuel type, burner capacity, number of burners, and whether the burner is forced draft or natural draft. Minimum controls found on all burners are:
  • Safety valve (steam) or safety relief valve (hot water) - make sure the safety relief valve is not stuck but lifts freely; leaking valves may indicate dirt on the valve seat that can be cleaned or a worn valve seat that must be replaced
  • Low-level cutoff - cuts off fuel in the event of low water level and requires manual reset to resume boiler firing
  • Flame scanner - shuts off fuel flow if burner flame is lost and requires manual reset to resume fuel flow
  • Temperature control (hot water) - turns burner on and off to maintain a set-point temperature
  • High-temperature cutoff (hot water) - if water temperature exceeds the high-temperature safety setpoint, shuts off fuel flow to the burner and requires manual reset to resume boiler firing
  • Pressure control (steam) - similar to the temperature control, but maintains a steam pressure setpoint
  • High-pressure cutoff (steam) - if steam pressure exceeds the high-pressure safety setpoint, shuts off fuel flow to the burner and requires manual reset to resume boiler firing.
  1. Make sure the boiler will pass the pressure test. Prior to draining the boiler for cleaning, fill it with water. With the boiler at operating pressure, close the valves to isolate the boiler from the system. If the pressure drops, the boiler will fail the inspection; so, fix the leaks. Start by checking the valves (isolation, drain, and water level) because they are most susceptible to small leaks that can cause the boiler to fail the test.
  2. Make sure the pressure gauges have been calibrated and are marked with the calibration date.
  3. Clean the boiler waterside. Draining and flushing the boiler will help remove scale and sediment.
  4. Make sure the proper American Society of Mechanical Engineers (ASME) stamp is installed on the boiler. ASME designators shown on the stamp are “U” for unfired pressure vessels, “H” for heating boilers, and “S” for power boilers.
  5. Make sure the water treatment system is working properly. Water treatment helps prevent problems resulting from scale buildup, sediment, and oxygen or carbon dioxide corrosion. Water from boilers that have been laid up for the summer months should he tested prior to putting the boiler back online. Boilers should not be drained during summer lay up to avoid corrosion. If a significant amount of water is added at any time, the water must be immediately heated to at least 180 degrees Fahrenheit to drive off dissolved gases from the water to avoid corrosion.
  6. Check for obvious defects, problems that should be identified and corrected such as unusual noises, deformed door gaskets, damaged insulation, or stains indicating leaks. Drains should be clean and clear and run freely.

Fuel oil-fired boilers are especially susceptible to corrosion on the fireside and leaks in the fuel train. If the boiler firing level is too low, condensation can occur in the stack and cause corrosion.

When bringing a boiler online with other boilers, make sure the operating temperature and pressure are the same as the other boilers online before opening the supply and return isolation valves. When bringing a boiler online, crack the valves and check for unusual noises or vibrations prior to fully opening the valves. For steam boilers, be sure to drain condensate from the steam feed line prior to opening the steam outlet valve to avoid slugging condensate into the steam main.

Combustion Analysis


DO NOT touch the Model 300 Combustion Analyzer probe after it is removed from a stack. Allow the probe to cool before handling.
When emptying filter/trap bowl and particulate trap, be aware that both traps may contain hot and mildly corrosive water. Take the necessary precautions to avoid being burned. All of the sensors contain corrosive chemicals. DO NOT puncture or take them apart.


To avoid damaging the probe assembly due to excessive heat, remove probe from stack at or before the prescribed time listed below. Allow probe to cool to room temperature before reinserting it back into the stack.

100–1,000°F (38–538°C)… Unlimited
1,000–1,200°F (538–649°C)… 30 mins. per exposure
1,200–1,400°F (649–760°C)… 10 mins. per exposure

Note that the high-temperature extended-probe options have unlimited exposure times up to 2,000°F (1,093°C).

  • Allow probe to cool before placing it in case.
  • DO NOT store the Model 300 Combustion Analyzer at temperatures below –4°F (–20°C).

Perform testing using the operating instructions that come with the analyzer.

Causes of Boiler Failures

Automatic low-high water control equipment must be serviced on a daily basis when the boiler is in operation. A high frequency of boiler failures is the result of low water, and can be attributed to a careless boiler operator. A procedure must be established at your facility to regularly clean the glass gauge column by “blowing down” the column at the start of the facility day, during non-peak operating periods, and at the conclusion of the facility day or shift. This ensures ability to determine the level of water in the boiler.

Low Water

A major reason for damages incurred to low-pressure steam boilers is the low water within the boiler. If the condition of low water exists it can seriously weaken the structural members of the boiler, and result in needless inconvenience and cost. Low-pressure boilers can be protected by installing an automatic water level control device.

Steam boilers are usually equipped with automatic water level control devices. It must be noted, however, that most failures occur due to low water on boilers equipped with automatic control devices. The water control device will activate water supply or feedwater pumps to introduce water at the proper level, interrupt the gas chain and ignition process when the water reaches the lowest permissible level, or perform both functions depending on design and interlocking systems. No matter how automatic a water control device may be, it is unable to operate properly if sediment scale and sludge are allowed to accumulate in the float chamber.

Accumulations of matter will obstruct and interfere with the proper operation of the float device, if not properly maintained. To ensure for the reliability of the device, procedures must be established in your daily preventive maintenance program to allow “blow-down” the float chamber at least once a day. Simply open the drain for three to five seconds, making certain that the water drain piping is properly connected to a discharge line in accordance with city building codes. This brief drainage process will remove loose sediment deposits, and at the same time, test the operation of the water level control device. If the water level control device does not function properly it must be inspected, repaired, and retested to guarantee proper operation.

Low Water Cutoff - Tests and Maintenance

There are two very effective tests for low water controls on steam boilers. The first is the quick drain or blowdown test, which should be performed at a time other than a peak steam generating period. As the water is drained from the column the firing sequence is interrupted, the low water alarm signal activates, and the boiler operation shuts down.

The second and more costly method is the slow-drain test. By opening the blowdown valves, the water level can be checked to determine the water level in the column, gauge glass, and boiler. The boiler should shut down while you determine the level in the gauge glass.

As a safety precaution, the low water float chamber of hot water boilers should be tested daily, at the beginning of the shift, at the end of the shift, and once during non-peak firing periods. Time of tests and the boiler controls tested should be recorded on your boiler room log.

Annually, or as required, a thorough inspection of all low water control parts shall be performed. The annual inspection should include opening and cleaning the water chamber.

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