Service and Maintenance of Boilers

There are many different makes of packaged heating boilers. Because their construction, firing equipment, and controls vary, the following instructions are provided as general guidelines. Be sure to consult the operating manual provided by the manufacturer. It will provide any unique instructions.

General Maintenance of Boilers

Always look for leaks in steam, water, and fuel connections. Do not allow these connections to leak for any length of time. The scouring action of the escaping fluid can cause the sealing surfaces to erode. Leaks should be repaired as soon as they are noticed. Periodically check the tightness of adjusting screws, locknuts, sheave setscrews, valve packings, and other fittings.

Inspect the boiler feed or circulating pump packing glands weekly. The gland nuts should be tightened only enough to prevent excessive leakage. Leakage of a few drops a minute, however, is desirable to prevent the drying out of packing and scoring of shaft. If the pump has a mechanical seal, it should not leak at all.

Washing Out the Boiler

After the first three months of operation, new boilers should be shut down, drained, opened up, flushed out with a high-pressure hose, and inspected. Thereafter this procedure should be repeated as often as conditions warrant. Tubes and tube sheets should be inspected for scale formation and pitting. This inspection will show the effectiveness of the water treatment.

Cleaning the Firetubes

Inspect the fireside of the tubes the first time the boiler is washed out. The tubes may have soot deposits in them as a result of incomplete combustion. If the tubes have soot in them, they must be cleaned. Tube cleaning is accomplished by opening the front and rear doors and brushing the tubes from either end. Remove all loose soot and accumulations. Always cover door gaskets with graphite and oil or an antifreeze compound before closing the doors. This makes the doors easier to open for future cleanings.

Lubrication in Boilers

Pump and fan motors may be equipped with either prelubricated bearings, sealed bearings, or standard ball bearings. Depending on the type of boiler, there may be fuel pumps, makeup water pumps, circulating pumps, and fresh air fans, each with an individual motor and drive that may require lubrication. The fresh air dampers may also require lubrication.

Sealed bearings don’t usually require additional lubrication for three years or more. Standard bearings normally require lubrication once a year. Follow the manufacturer’s recommendation as to the frequency of lubrication and lubricant required.

Refractory Maintenance

Inspect the refractory each time the boiler is opened for cleaning. Regularly wash-coat the refractory with a diluted heat-resistant cement to prolong its life. Joints and cracks should be faced with the cement as well; otherwise, extensive damage can occur.

If segments of liners become burned out or broken, replace them with the same kind of material. If general deterioration of the refractory becomes apparent, it will be necessary to replace the refractory.

Burner Maintenance

Be sure to observe the burner flame regularly during operation. A symmetrical flame is a good indicator of a clean burner; a distorted flame indicates a dirty burner. Gas burners rarely cause problems and should not require cleaning and inspection more than once a year. Oil burners however, should be periodically cleaned. To clean the oil burner, remove the burner assembly from the front of the boiler. Dismantle the burner nozzle and clean it thoroughly, following the manufacturer’s directions.

Clean the diffuser, pilot tube, and igniter. Run a cloth through the scanner tube to maintain a shining surface. Wipe the rotary damper and make sure it moves freely. Check the electrode setting of the pilot to make sure it is still correct.

Electrical Control Maintenance in Boilers

Motor Starter Maintenance
Ordinarily, motor starters require no maintenance other than occasionally blowing out the dust, since dust may cause excessive heating and contact wear. Never file the contacts. Filing removes the silver coating of the points, which can cause operational problems.

Programming Control Maintenance
The programming control requires no maintenance other than to blow out any accumulated dust. Never file any contacts. If the contacts look dirty or slightly oxidized, clean them by drawing a piece of hard-finished paper between the contacts.

Always keep the scanner lens clean—even a small amount of contamination will reduce the flame signal to the lead-sulfide photo cell. Wipe the lens clean with a soft cloth. When operated within reasonable temperature limits, the cell has an estimated life of 20,000 hours.

Since high humidity can cause high resistance leakage in the electric circuit, it is best to leave power on the control even when the boiler is not in use. However, be sure to block the fuel supply to avoid unintentional startup. Test the flame failure device and programming control regularly to assure they are operating properly. Do this by simulating a flame failure during boiler operation by shutting off the fuel supply or by removing the scanner from the sighting tube. The flame failure relay should drop out and the main electric fuel valve should close within four seconds. The alarm circuit will be energized following the safety lockout. To restart the boiler, open the manual gas valve or insert the scanner into the tube and push the reset button. Always allow the warp element of the lockout switch to cool for at least two minutes before resetting.

Modulating Pressure Control Maintenance
Other than blowing out the dust with compressed air at regular intervals, no field maintenance is recommended on the modulating pressure control.

Modulating Motor Maintenance
The modulating motor is a sealed unit; do not attempt maintenance on it. If the unit malfunctions, replace it with a similar, functioning unit.

Oil Solenoid Valve Maintenance
The oil solenoid valve should be occasionally dismantled and cleaned. Follow the manufacturer’s instructions for cleaning.

Gas Solenoid Valves Maintenance
Gas solenoid valves normally do not require maintenance. If a valve becomes inoperative, the cause is most likely a defective or burned-out coil that needs to be replaced.

Electrical Wiring Maintenance
Electrical wiring on boilers can deteriorate from high temperatures and vibration. When it becomes necessary to replace some of the wiring, use a qualified electrician. Electrical wiring on boilers must conform with the standards laid out in electrical codes.

Miscellaneous Equipment in Oil- Fired Burners

The metering, or control, valve does not require any routine maintenance. However, if the valve becomes clogged, it will have to be disassembled and cleaned.

The pressure setting of the back pressure return valve can be increased or decreased by moving the adjusting screw into or out of the spring casing. If the fuel pressure becomes erratic, dismantle and clean the valve. Check the diaphragm for soundness before reassembling the valve.

For boilers equipped with air atomizing oil burners:

  • Oil bath air filter (air pump intake): Service this unit regularly according to the directions given on the air filter. Change the oil at regular intervals and maintain it at the indicated level.
  • Air pump: No maintenance is recommended. If the unit becomes inoperative, return it to the factory or dealer for repair or replacement.
  • Air pump oil filter assembly (air pump discharge): The strainer in the lube oil filter should be removed and cleaned once a month.
  • Oil heater: The steam or electric heating elements of heaters used for heavy fuel oils should be cleaned yearly. If the heater acts sluggish, it needs to be cleaned more often. Any accumulation of carbonized oil or other residue should be removed. Inspect the heater tank each time the element is removed and flush out all accumulated sludge before reinstalling the heater. The thermostats that control the heater operation cannot usually be serviced in the field other than keeping the temperature adjustment dust-free.

V-Belt Maintenance

The V-belt drive doesn’t require servicing. Check the tension of belts at different spots on the belts—wear and stretch may cause slacking. Adjust the tension when necessary, but avoid overtightening. If the top of the V- belt is riding down in the pulley, replace the belt. Don’t use any dressing compound.

This article is adapted from BOMI International’s course Boilers, Heating Systems, and Applied Mathematics, part of the SMA and SMT designation programs. More information regarding this course or the new High-Performance certificate courses is available by calling 1-800-235-2664. Visit BOMI International’s website,