How To Repair Oil Furnaces
How To Repair Oil Furnaces

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.

An oil furnace is a complex assembly. The maintenance and repair work for this type of furnace is limited to simple parts: the filters, the blower, the motor belts, the switches, and the thermostat. Electrodes, an oil nozzle, air tubes, a transformer, a pump, and other components require special tools and testing equipment and are best left to a professional for service.

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.

There's not much you can do to fix an oil furnace, but routine maintenance can forestall many problems. On the next page you'll find a list of tips to keep your furnace running smoothly.

Oil Furnace Maintenance Tips
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:
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.
If your furnace still isn't working, use the handy troubleshooting chart on the next page to find a solution.

Troubleshooting Oil Furnaces and Oil Heaters
Cleaning or replacing filters is a job anyone can do, and often it's the reason an oil furnace isn't performing at peak levels. Use this chart to see if the problem with your furnace might be fixed with a filter change.


Problem Possible cause Solution
Furnace won't run

1. No power.

1. Check for blown fuses or tripped
circuit breakers at main entrance
panel or at separate entrance panel;
restore circuit.
2. Switch off.
2. Turn on separate power switch on
or near furnace.
3. Motor overload.
3. Wait 30 minutes; press reset button.
Repeat if necessary.
4. No fuel.
4. Check tank; if necessary, refill tank.
5. Fuel line blockage.
5. Clean oil filter and oil pump strainer.
If problem persists, call a
Burner won't fire 1. No fuel. 1. Check tank; if necessary, refill tank.
2. No ignition spark.

2. Press reset button on stack control;
if necessary, clean stack control.
If no result, call a professional.
If furnace has electric-eye safety,
clean safety; if no result, call a
Not enough heat
1. Thermostat set
too low. 1. Raise thermostat setting 5°.

2. Air filter dirty. 2. Clean or replace air filter.
3. Blower clogged. 3. Clean blower assembly.
4. Registers closed
or blocked.
4. Make sure all registers are open;
make sure they are not blocked by
rugs, drapes, or furniture.
5. System out of
balance. 5. Balance system.
6. Blower belt loose
or broken. 6. Adjust or replace belt.

7. Burner dirty. 7. Call a professional.
Furnace turns
on and off
repeatedly 1. Air filter dirty.
2. Oil filter dirty.
3. Motor and/or blower
1. Clean or replace air filter.
2. Clean or replace oil filter.
3. If motor and blower have oil

needs lubrication.
ports, lubricate.
4. Blower clogged.
4. Clean blower assembly.

5. Stack control faulty. 5. Call a professional.

Blower won't
1. Blower control
1. Reset thermostat from ON
stop running set wrong. to AUTO.

2. Limit switch set
wrong. 2. Reset limit switch.
Furnace noisy
1. Access panels loose.
1. Mount and fasten access
panels correctly.
2. Belts sticking, worn,
or damaged.
2. Spray squeaking belts with fan
belt dressing; replace worn
or damaged belts.
3. Blower belt too
loose or too tight. 3. Adjust belt.

4. Motor and/or blower
needs lubrication. 4. If motor and blower have oil
ports, lubricate.
5. Burner dirty. 5. Call a professional.

Oil filters should be changed twice a year. Find out when and how to do it on the next page.

How To Clean and Replace Oil Furnace Filters

What You'll Need
You'll want to have these tools on hand to clean the pump strainer:

Old, soft toothbrush
Replacement pump strainer and gasket

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.

Some oil furnaces have a pump strainer, which is located on the pump attached to the burner/ blower unit. Clean this strainer when you clean the oil filter. Here's how:

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.

Step 3: Soak strainer in kerosene for several minutes to loosen any built-up sludge. Carefully clean strainer with old, soft toothbrush.

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.

Sometimes the problem is not in the filter but the stack control, a safety device that shuts down the furnace. Find out how to check it and what to do about it on the next page.

How To Clean the Oil Furnace Stack Control

What You'll Need
You'll want to have these tools on hand to check the stack control:

Soapy water
Soft cloth
Refractory cement

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.

If the burner fails to ignite, first check the fuel tank and refill it if necessary. If the tank doesn't need to be refilled, press the reset button on the stack control. If the burner doesn't ignite after you've pressed the button once, clean the control, as detailed below. Then press the reset button again. If the burner still doesn't operate, call a professional service person.

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.

Some oil furnaces have an electric-eye safety switch instead of a stack control. This switch serves the same function as the stack control. If the burner has an electric-eye safety, remove the access cover over the photocell; it is held by hooks or retaining screws. Wipe the cover clean to remove accumulated soot. Reassemble the switch, replace the cover, and turn the power back on. If the burner still doesn't ignite, call a professional service person.

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.

You can, though, set the switches, which must be ON for the furnace to operate. Find out where they are located on the next page.

Switches, Draft Regulator, and Controlling the Burner
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.

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.

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.

Burner Adjustment

Do not try to adjust the burner of an oil furnace; call a professional service person.

Although you cannot fix major problems with an oil furnace, with the information in this article you now have the know-how to handle most of the problems that will come your way.

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