How to Service a Furnace
Furnaces & More |
Cleaning a Furnace
Dirt is the biggest enemy of your furnace. It can waste fuel and drastically lower efficiency. Dirt affects all three basic components of your furnace, so cleaning is the most important part of regular maintenance. The three parts of the furnace should be cleaned: the filter system, the blower, and the motor.
The furnace filter should be replaced or cleaned at the beginning of the heating season and about once a month during periods of continuous use. To check the filter, take it out and hold it up to the light. If it looks clogged, replace it with a new filter of the same type and size regardless of the length of time it has been used.
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A permanent filter is usually sprayed with a special filter-coating chemical, available at hardware stores and home centers. Clean this type of filter according to the manufacturer's instructions, which are usually attached to the furnace housing. Here's how to replace a filter:
Step 1: Look for metal panel on front of furnace below return-air duct, between duct and blower system. Panel may be marked filter, or it may form lid or front of boxlike projection on furnace housing.
Step 2: Slip panel off its holding hooks, or unscrew panel from box or furnace housing. On some heating units, filters are exposed; just slip filter up and out of U-shape tracks that hold it in place.
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Step 3: Inspect and replace or clean filter, depending on type.
Step 4: Clean blower assembly, belts and pulleys to blower, and motor housing. Cleaning blower is critical if furnace has a squirrel-cage fan, because openings in this type of blower often become clogged with dirt. To clean blower, remove panel that covers filter to gain access to blower or panel on front of furnace. This panel may be slip-fit on hooks or held by series of retaining screws. Access to inside of blower is usually gained by sliding out fan unit, which is held on track by screws.
How to Troubleshoot a Gas Furnace
Natural gas and propane burn cleaner than fuel oil, and most gas furnaces present fewer operational difficulties than oil burners do. In fact, the problems that affect gas furnaces typically involve the furnace's thermocouple, the pilot light, or some component of the electrical system.Gas furnaces and heaters have control shutoffs to prevent gas leaks, but they are not fail-safe. If you smell gas in your house, do not turn any lights on or off, and do not try to shut off the gas leading to the furnace. Get out of the house, leaving the door open, and immediately call the gas company or the fire department to report a leak. Do not re-enter your home.
 © 2006 Publications International, Ltd. Most natural gas furnaces have few operational difficulties. Problems typically involve the pilot light, the thermocouple, or some part of the electrical system. |
The pilot light controls, reset buttons, gas valves, and thermocouple are usually contained in an assembly at the front of the furnace. The furnace limit switch is located on the plenum (main chamber) or main duct junction on the upper housing of the furnace.
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The pilot light on a gas furnace can go out because of drafts. To relight the pilot, follow the manufacturer's instructions exactly; they are usually fastened to the furnace. If instructions for relighting the pilot are not provided, follow this general procedure:
Step 1: Find pilot light assembly. It typically has a gas valve with on, off, and pilot settings.
Step 2: Turn valve to off and wait three minutes.
Step 3: Switch valve to pilot setting. Hold lighted match to pilot opening while you push reset button on pilot control panel. Keep this button depressed until pilot flame burns brightly, then set valve to on position.
Step 4: If pilot flame won't stay lit, opening may be clogged. Turn gas valve off, and clean opening with piece of fine wire. If it won't stay lit after several attempts, you may have faulty thermocouple. If pilot flame still won't stay lit, call professional service person.
Some furnaces have an electrical system to ignite the gas; in these systems there is no pilot light. Instead, an electric element heats up and ignites the burners. If this electric ignition system malfunctions, call a professional service person.
Replacing the Thermocouple
The thermocouple is a gas furnace component located near the pilot light burner. It is a safety device that shuts off the gas if the pilot light goes out or the electric igniter fails.
If the pilot light won't stay lit, the thermocouple may be faulty and should be adjusted or replaced. To adjust the thermocouple, you must tighten the thermocouple nut with a wrench. Take care not to apply too much pressure to the nut -- just tighten it slightly. Then try lighting the pilot. If the pilot won't stay lit, replace the thermocouple with a new one of the same type. Here's how to replace a thermocouple:
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Step 2: Insert new thermocouple into hole in bracket. Be sure steel tube is up and copper lead is down. Under bracket, screw bracket nut over tube. Push connection nut to threaded connection where copper lead connects to gas line. Make sure connection is clean and dry.
Step 3: Tightly screw nut into place, but do not over-tighten. Both bracket nut and connection nut should be only a little tighter than if hand-tightened.
 © 2006 Publications International, Ltd. The thermocouple is installed next to the pilot light. A bracket holds it in place, steel tube up and copper lead down. |
The limit switch is a safety control switch located on the furnace just below the plenum. If the plenum gets too hot, the limit switch shuts off the burner. It also shuts off the blower when the temperature drops to a certain level after the burner has shut off. If the blower runs continuously, either the blower control on the thermostat has been set to the ON position or the limit control switch needs adjustment. Check the thermostat first. If the blower control has been set to ON, change it to AUTO; if the blower control is already on AUTO, the limit switch needs adjusting.
Care Guide |
Burner Adjustment
The flames on the gas burner should be full and steady, with no sputtering and no trace of yellow. To adjust the flame height on the main burners, call a professional service person. To adjust the height of the pilot flame, turn the flame adjustment screw until the flame is from 11/2 to 2 inches high. The adjustment screw is located near the gas valve on the pilot assembly, if the control has this adjustment feature.
Gas Leaks
If you suspect leaks around the furnace unit, stir up a mixture of liquid detergent and water. Paint this mixture on the gas supply line along its connections and valves; the soapy water will bubble at any point where there's a leak. If you find a leak, try tightening the leaking connection with a pipe wrench, but be careful not to overtighten the connection. If the pipe connections or valves still leak, call a professional service person.
An oil furnace has an entire new set of the problems from the ones we've just conquered in gas furnaces. Move on to the next section to learn how to clear a blocked fuel line or change an oil filter.
How to Troubleshoot an Oil Furnace
Oil-fired burners are used in many parts of the country as the basic heat source for warm air and hot water heating systems. Most of the home oil systems in use today are called pressure burners. In this type of system, oil is sprayed into a combustion chamber at high pressure, propelled by a blower, and ignited by an electric spark.The oil continues to burn as the mist is sprayed. While there aren't many quick fixes you can undertake yourself on these types of furnaces, good regular maintenance can help eliminate many problems. Here are a few oil furnace maintenance tips:
From annoying noise to low heat, there are many problems that can strike your oil furnace. Click here for instructions on how to deal with specific issues. |
- During the heating season, check the smoke from the chimney. If the smoke is black, the furnace is not burning the oil completely and fuel is being wasted. Call a professional service person for adjustments.
- Clean the blower at the beginning of the heating season and again about midway through the season.
- Clean soot from the stack control about midway through the heating season.
- If the blower motor has grease or oil fittings, lubricate the fittings midway through the heating season with cup grease or 10-weight nondetergent motor oil (not all-purpose oil), available at hardware stores.
- Clean the thermostat before each heating season.
© 2006 Publications International, Ltd.
Most oil furnaces in use today are called pressure burners. In this type of system,
oil is sprayed into a combustion chamber at high pressure.
To become familiar with your oil furnace, remove the access panel covering the burner blower by removing the retaining screws around the rim of the housing. You can access the air blower and filter through a metal panel on one side of the furnace. The panel is held by either hooks or retaining bolts; slip the panel up and off the hooks or remove the bolts and lift the panel off. Most furnaces have switches and reset buttons located on the motor or in a switch box outside the furnace housing. These are usually identified with stampings or labels, such as DISCONNECT SWITCH, RESET, and so on. The stack control sensor, a safety device that monitors burner operation, is positioned in the stack and held with a series of retaining bolts.
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The oil filter should be changed or cleaned at the start of the heating season and about midway through the season. Here's how to clean or replace the filter:
Step 1: Close oil shutoff valve between fuel tank and filter.
Step 2: Unscrew bottom or cup of filter housing, and remove filter.
Step 3: If filter is disposable, insert new one of same size and type. If furnace has permanent filter, clean filter according to furnace manufacturer's recommendations.
Step 4: Replace old filter gaskets with new ones.
Step 5: Screw in bottom of housing, and open oil shutoff valve.
 © 2006 Publications International, Ltd. Clean the pump strainer after cleaning the oil filter. To reach the strainer, unbolt the cover of the pump housing and lift off the cover. |
Step 1: Unbolt cover of pump housing (where oil line enters burner), and lift off cover.
Step 2: Remove thin gasket around rim. Find and remove strainer, which is a cylindrical or cup-shape wire mesh screen.
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Step 4: Inspect strainer. If it's torn or badly bent, replace it with new pump strainer of the same type.
Step 5: Set strainer into place on pump, place new gasket on rim, and bolt cover of pump housing back on.
Switches
Some oil furnaces have two master switches. One is located near the burner unit, and the other is near the furnace housing or even at a distance from the furnace. Make sure these master switches are both turned to the ON position.
Stack Control
The stack control of the oil furnace, located in the stack, is a safety device that monitors the operation of the oil burner. If the burner fails to ignite, the stack control shuts off the motor. Frequently, however, a furnace shutdown is caused by a malfunctioning stack control rather than by the burner.
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The stack control gradually becomes coated with soot during the heating season. To keep it working properly, clean the control every month or as soon as it becomes soot-covered. Here's how to clean the stack control:
Step 1: Remove bolts that hold control in stack. Pull out sensor and its housing.
Step 2: With brush dipped in soapy water, remove all soot from control. Wipe control dry with soft cloth.
Step 3: Before replacing control, clean stack. Spread newspaper to protect floor, then disassemble stack. As you work, remove soot and debris from each section by tapping them firmly on newspaper-covered floor.
Step 4: After cleaning sections, reassemble them in reverse order. Make sure stack sections are properly aligned and firmly connected.
Step 5: Finally, reposition stack control in stack, and reseal connection to chimney with refractory cement.
 © 2006 Publications International, Ltd. Clean the stack control every month. To remove the control, turn off the power to the furnace, then back out the bolts that hold it in the stack. |
If the stack control or electric-eye safety switch is especially dirty, the furnace may not be properly set to burn the fuel completely. In this case, call a professional service person for adjustment.
Caution: Do not attempt to replace these controls yourself.
Draft Regulator
The draft regulator, located on the stack, is closed when the burner is off but opens automatically to let air into the chimney when the burner is turned on. Accumulated soot and rattling are signs that the draft regulator needs to be adjusted. Too much air in the chimney wastes heat; too little air wastes fuel by failing to burn it completely. To increase the airflow, screw the counterweight inward. To decrease airflow, turn the counterweight outward. The draft regulator should be adjusted by a professional service person as part of regular annual maintenance.
Limit Switch
The limit switch is a safety control switch and is located on the furnace just below the plenum. If the plenum gets too hot, the limit switch shuts off the burner. It also shuts off the blower when the temperature drops to a certain level after the burner has shut off. If the blower runs continuously, either the blower control on the thermostat has been set to the ON position, or the limit control switch needs adjustment.
To determine the problem, check the thermostat. If the blower control has been set to ON, change it to AUTO; if blower control is already on AUTO, the limit switch needs adjusting. To do this, remove the control's cover and find the toothed dial underneath. One side is marked LIMIT; don't touch this side. The other side is marked FAN. There are two pointers on the fan side; the blower turns on at the upper pointer setting and shuts off at the lower pointer setting. Pointers should be set about 25 degrees apart. Set the upper pointer at about 115 degrees Fahrenheit and the lower one at about 90 degrees Fahrenheit.
Burner Adjustment
Do not try to adjust the burner of an oil furnace; call a professional service person.
Finally, we have electric furnaces and heaters. Electric heat is in some ways much simpler than either gas or oil, but it can still have its fair share of problems. Keep reading to the next section to learn how to maximize the efficiency of your electric furnace.
How to Troubleshoot an Electric Furnace
Although an electric heating system does have advantages, its operating cost generally makes it less desirable than any of the other furnace systems available today. The high cost means that minimizing heat loss caused by improperly installed ducts or inadequate insulation is even more important than with other types of systems.
 © 2006 Publications International, Ltd. Electric furnaces use heating elements controlled by relays to warm the air. The elements are fused on a separate panel. |
Care Guide |
Fuses
Electric furnaces are fused at a building's main electrical service entrance. Many electric furnaces are on separate circuits, sometimes located in a separate fuse box away from the main panel. The heating elements of the furnace are also fused, and these fuses are located on a panel that is on or inside the furnace housing.
 © 2006 Publications International, Ltd. The heating elements on an electric furnace are fused on a separate panel located on or inside the furnace housing. |
Now that we've run the entire furnace gamut, your home should be nice and toasty all winter long. Though major furnace repairs to a furnace are best left to a professional, you should be able keep those house calls to a minimum with our maintenance tips.
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