Oil Furnace Repair

Fortunately, an oil furnace is simple in operation and relatively trouble free. When it’s not, it’s time to fix it — or call someone who can. This Fix-It Guide on oil furnace repair tells how an oil furnace works, what often goes wrong, how to identify an oil furnace problem, and what parts and tools you will need to fix it. It then gives simple step-by-step instructions for how to clean or replace an oil furnace filter. For some repairs, you will be referred to switch repair, electrical service panel, motor repair, or forced-air distribution system repair.

How Does an Oil Furnace Work?

Oil Furnace Repair

An oil furnace is similar to other types of furnaces. The main difference is that heating oil fuels the burner that heats the air.

An oil furnace uses a low-grade petroleum derivative as fuel to heat air, hot water, or steam. An oil forced-air system (OFA) includes the blower and ducting to distribute the heated air throughout the house. Modern home oil systems use pressure burners. Oil is sprayed into a combustion chamber at high pressure, propelled by a blower and ignited by an electric spark. The oil burns as the mist is sprayed. These units are more efficient than older models.

What Can Go Wrong with an Oil Furnace?

Oil burners are generally quite reliable. Routine maintenance is the key to avoiding expensive repairs. And there are several things you can do before calling for repair service. The burner may not run, or may run but not fire. The burner may cycle too often or it may smoke or squeal. The chimney may smoke.

Fix-It Tip

When buying replacement filters, buy enough for a few years at once so you have them on hand. And when you change the filters, write the date on the filter or on a tape stuck to the outside of the furnace so you can determine when to next replace it.

How Can I Identify an Oil Furnace Problem?

  • If the burner doesn’t run, set the thermostat a few degrees higher than normal to see if it comes on. If it still doesn’t come on, check switches, and breakers and fuses (see the Electrical Service Panel Fix-It Guide). If the unit has a reset button, press it. Also oil the motor at any oil ports (see below).
  • If the unit doesn’t want to start and run, first check the electrical service panel to make sure that the ignition is getting power. If there is power, check the built-in safety controls (see below) that may turn the system off if they perceive problems.
  • If the burner cycles too often, replace the filter (see below). Also, oil and adjust the blower (see the Forced-Air Distribution Fix-It Guide).
  • If the burner runs but won’t fire, make sure the oil valves are open and that there’s oil in the tank. Check the tank level with a clean stick.
  • If the burner smokes or squeals, shut off the unit, let it cool, and fill the oil cups. Recheck them after the motor has run for an hour.
  • If the chimney smokes even after the flue has warmed up, the unit is wasting fuel; call for professional repair.

Safety Controls

Oil furnaces and other heat systems include safety devices that monitor operation and turn off the unit if something goes wrong. In some cases, the safety device can be the problem.

  • If you encounter an operating problem with an oil furnace, first reset the safety and try again.
  • If the burner kicks off again, shut off all power at the electrical service panel; the burner motor and ignition may be protected by separate fuses or breakers.
  • If the sensor has a photocell, wipe it with a clean rag or tissue and see if the furnace starts.
  • If the safety is a stack switch mounted on the flue, remove the screw holding the unit to the stack, slide it out, and wipe off the sensor.
  • If the furnace won’t start after three tries, seek professional assistance. Unburned oil can accumulate in the combustion chamber and “flash back.”

Fix-It Tip

At the beginning of the heating season and every month or two during it, inspect the oil heating system for filter condition and clean as needed. In addition, older furnaces require the burner Motor to be lubricated periodically. Newer units have permanent lubrication. You can tell which your system has by looking for oil ports where the lubricant, a few drops of light, non-detergent oil, is added.

What Do I Need for Oil Furnace Repair?

Some replacement parts for oil furnaces can be found at larger hardware stores, and others are available through your fuel dealer or its supplier. Ask. The tools you’ll need for fixing an oil furnace include these:

  • Screwdrivers
  • Wrenches
  • Replacement filter
  • Lightweight lubricating oil
  • Vacuum cleaner

What Are the Steps to Oil Furnace Repair?

Clean or replace an oil furnace filter:

  1. Open or remove the blower access door, typically located on the front or side of the furnace housing.
  2. Remove the filter; some slide out while others are pressed into place.
  3. Use a vacuum cleaner to remove dirt and dust from the area around the filter. Some units have a dry-foam filter that also needs periodic vacuuming.
  4. Replace the filter with one of the same dimensions and density, preferably the model suggested by the manufacturer.
  5. Close or reinstall the blower door, making sure that any interlocks are in the correct position to operate.

Fix-It Tip

Just before the heating season starts, make sure you inspect the chimney and flue for air leaks and pests (animal and bird nests). Repair any cracks. Test for air leaks by using a burning candle.