Trouble Shooting Your Oil Furnace

Whatever you do, don’t hit the reset button on your oil furnace more than twice.

Close of up of oil drops | Troubleshooting Oil Furnace
Image: Mac99/Getty

An oil-burning furnace is essentially a blowtorch in a fireproof box. Electrical ignition sparks a high-pressure mist of oil and air, heating the air in an adjacent chamber. A blower pushes the warmth throughout your home.

Despite its complexity, problems with an oil-burning furnace are rare. The good news is that many common problems can be addressed easily by a homeowner. However, some repairs call for an HVAC professional.

Start Out Easy

  • Check the thermostat. Is the fan mode set to “automatic?” Is the thermostat set to “heat?”
  • Check your fuel oil supply. Don't just rely on the gauge — it’s as prone to failure as any component. Unless you just had it filled recently, check the fuel tank itself. Use a dipstick to determine how much fuel you have. By the way, it's never a good idea to let your fuel level get low; that's when sludge and sediment get sucked into lines and plug up filters.
  • Inspect the furnace. Can you hear it running? Is the cabinet warm to the touch? The air filter may simply be so dirty it's blocking the flow of warmed air. Remove the filter. Problem solved? Great. Install a clean filter ($3-$30, depending on make and model furnace) and bask in your good fortune.

In rare cases, clogged ducts can restrict air flow sufficiently to reduce the performance of your furnace. Duct cleaning is dirty work that’s best left to professionals. 


Still Not Working? Try These Steps

If the furnace isn't running, go back to the thermostat and crank it up by 5 or 10 degrees. Does the furnace start? If not, switch the fan setting from “automatic” to “on” or “run.” If air isn’t moving and the furnace fan isn’t running, check your circuit breaker. If the circuit breaker is tripped and resetting it only causes it to trip again, have an electrician check the wiring and circuit capacity.

If the fan is running, your circuit is fine. Next step: Look for the “reset” button on the furnace control module. Popped up? Your problem may be fuel-related -- either a lack of supply or an obstruction in its flow. Press the reset button and check your oil tank and in-line filter. Clean or replace the filter ($4-$7) if it's gunked up.


Don't hit “reset” more than twice. The process pumps oil into the burner chamber, where it can accumulate if you have no ignition. Then when the furnace finally does start, it can do so explosively. So if the button won't reset, or quickly pops up again, it's time to call a professional repair service. 

As you examine your furnace system, watch for two potential culprits: Leaks in oil lines and soot in the burner chamber. Leaks let air into the system, which can hurt performance. And soot indicates inefficient combustion that can lead to other problems. Either condition should be corrected by an expert.

When It Sounds Like Trouble

  • Knocking sounds: You likely have air in the lines. Purging the air -- called bleeding the lines -- isn't difficult, but it can frustrate a beginner. If you’re not confident, have your system checked over by a service pro.

  • Clattering sounds: Check the access panels on the furnace itself. They can work loose and rattle, with the annoying sound carried through the house on warm air from the furnace.
  • Squealing sounds: Probably indicate problems with a belt or the blower motor. Shut down the furnace, check the belt, and put just a few drops of electric-motor oil in any oiling ports on your firing assembly fan (some sealed units run oil free, so you may not have ports).
  • The furnace sounds like it's running intermittently: Check the air filter first. Then check your oil supply and filter. If the tank is full and the filters are clean, it's time for a service call focusing first on the burner nozzle and electrodes that ignite the fuel.

What Does a Professional Cost?

Expect to pay $80 to $120 per hour for professional help. On the upside, these folks work quickly. Typical service calls last only an hour or two (less if you stay out of the way).

And if the word from the pro is, “It’s gotta go,” consider alternatives, such as converting your oil-burner to a gas furnace.

Your Best Defense Against Problems

  • Prevent breakdowns with regular maintenance.
  • Replace filters at least twice a year ($10 to $20 each).
  • Vacuum the blower wheel ("squirrel cage") and clean dust and crud away from the electric eye sensor.
  • Replenish fuel oil regularly to keep levels high.
Larry Erickson
Larry Erickson

Larry Erickson is a features writer and essayist for newspapers and magazines. He has edited home improvement books for Better Homes and Gardens, The Home Depot, Stanley, and the Discovery Channel. He tends to a house and recalcitrant tractor in rural Iowa.