Although a gas-fired water heater is prone to few performance problems, periodic cleaning extends the life of the appliance and keeps the unit operating at peak efficiency. Maximize heat transfer by flushing the water heater's tank out once a year; this will remove insulating sediment from between the combustion chamber and the contents of the tank. Vacuum soot and ash from the combustion chamber and clean the main burner head every three to four months. Doing so will promote cleaner burning and keep your gas bills to a minimum.
Extinguish ignition sources in the vicinity of the water heater. Open doors and windows to ensure proper ventilation. Do not smoke while carrying out maintenance on your water heater.
Turn the gas burner control knob to the "off" position, then turn off the shutoff valve on the gas supply line where it comes into the wall or floor. Allow time for the combustion chamber to cool completely.
Undo the three different-size hex-head brass connections securing the thermocouple, manifold tube and pilot tube from the bottom of the gas valve, by turning them counterclockwise with an adjustable wrench. This will cause a small amount of trapped gas to escape. This small amount of gas will dissipate and will not be a concern. If a smell of gas persists, call the utility. Take care not to damage the tubes by forcing them or bending them too far.
Remove the outer door from the base of the water heater to reveal the burner tubing and ignition system. If the gas valve is labeled "White Rogers," there will be an orange wire leading to the piezo igniter. Remove the igniter by sliding it back toward the tank; leave the orange wire in the door assembly. If the heater is fitted with a "Robert Shaw" gas valve, undo the igniter valve terminal from the base of the igniter button with a screwdriver.
Unscrew the two nuts on either side of the manifold door with a nut driver. Remove the door while taking care not to damage the white gasket between the door and the manifold.
Slide the burner assembly and burner tube from the combustion chamber slowly and carefully. Try not to dislodge any scale or debris, and be careful not to damage the white gasket while doing so.
Clean the burner ports by brushing loose debris out with an old toothbrush. Fit a brush attachment to the vacuum cleaner hose and clean the entire assembly, including the inside of the combustion chamber and the exposed portion of the circular flame arrestor situated below the burner. Clean the cavity between the burner and the flame arrestor with the flame arrestor cleaning attachment provided with the water heater. Wipe the underside of the flame arrestor clean with a damp rag.
Inspect the sides of the fan-shaped radiation shield between the burner and the flame arrestor. If the side of the radiation shield is resting on the base, it will disrupt airflow. Install three 1/4-inch-high "feet" between the flame arrestor and the base to provide sufficient combustion air to the burner. These spacers are obtainable free of charge from the manufacturer.
Remove the clip-on perforated air intake screen from the base of the heater. Clean out all dust and debris from under the burner with a vacuum cleaner. Replace the screen.
Slide the burner assembly back into the heater. Seat the burner tube in its positioning bracket while doing so.
Inspect the white inner door gasket for wear. Replace it if necessary. Place the inner door over the two studs and settle it flush with the gasket. Replace the two nuts loosely.
Reattach the thermocouple, manifold tube and pilot tube connections; tighten the couplings with an adjustable wrench. Replace the piezo igniter or igniter valve terminal wire. Tighten the two inner door nuts with a nut driver. Replace the outer door.
Turn the main gas shutoff valve back on. Light the pilot flame by following the directions in the owner's manual. Turn the gas burner control to the "on" position to fire up the water heater.