3 (Potential) Reasons Your Heating Oil Furnace Won't Start

If you're a first-time owner of a home that uses heating oil, you might feel like your furnace operates on black magic. While combustion in a natural gas furnace is relatively straightforward, heating oil furnaces need specialized equipment to pump and vaporize the heating oil before it ignites. These extra components can make these systems seem intimidating to non-professionals.

Of course, you probably don't care much about that extra complexity if your furnace won't fire up—you just want to heat your home! If your heating oil furnace is stubbornly refusing to start, here are three potential reasons why this failure may be occurring. 

1. There's No Power to the Furnace

Despite the name, heating oil furnaces can't operate without electricity. Your furnace uses electricity for several components, including the draft inducer, oil motor, and main house blower. Without electricity, your furnace will not even begin its startup sequence, and you'll likely notice nothing happening when the thermostat should be calling for heat.

When there's no sign of life at all from your furnace, here are three easy questions to ask:

  • Is your thermostat setpoint higher than the ambient temperature in your house?
  • Is the furnace shutoff switch flipped to the "on" position?
  • Have you checked the fuse or breaker for the furnace?

If these simple diagnostic checks don't help, you'll want to contact a professional to investigate the problem further.

2. There's a Cad Cell Problem

The cadmium sulfide (cad) cell is the method that oil-burning furnaces use for flame rectification. This cell detects the presence of a flame for the burner, allowing the system to ignite and continue operating. If this cell doesn't detect the light from an active flame, the furnace will shut down to prevent spraying unburnt fuel into the combustion chamber.

Numerous steps are required to test a cad cell and confirm that it's at fault, so this isn't an issue you'll want to resolve yourself. However, you can try pressing the large red reset button on top of the cad cell to reset the unit. If the button doesn't stay down (or stays down briefly and pops back up), you should contact an HVAC technician for additional help.

3. There's an Internal Motor Problem

In some cases, the issue may be the oil motor itself. Several internal parts can fail on oil motors, although these devices are typically long-lasting and durable. Your motor may have a manual reset switch (not all do) separate from the reset switch on the cad cell. If this switch immediately pops back out, there's a high likelihood that the motor has an internal issue and cannot start.

The motor is one of the more expensive components on your furnace, so it's not something you'll want to diagnose yourself or replace blindly. If your motor is seemingly at fault, stop using your furnace to avoid more potential damage and call in a professional.

Contact a local heating service to learn more.