Oil furnace Troubleshooting

Solving Common Issues

HVAC For Beginners

Furnace Basics

Maintenance Guide

Product Reviews

This oil furnace troubleshooting guide will allow you to diagnose and repair the typical problems on a furnace that burns fuel oil or waste oil. The average service call will cost you over $100. We will help you to keep that money!


Before proceeding with diagnosing a problem with your furnace, you should ensure that the air filter is clean. (This is the biggest cause of furnace repair calls.)

Does the fan start?

If your furnace does not start, you can begin your diagnosis at the thermostat. Ensure that the thermostat is on heat and the setpoint is above the actual room temperature. Next, you can turn the fan from auto to on.

If the fan does no come on, you should check the breaker or fuse for the furnace. If the breaker is tripped or the fuse is blown, you should check the furnace wiring for signs of damage and then reset the breaker.

If the breaker was not tripped, the problem could be the primary control, the thermostat, blower motor, fan timer control, or it's run capacitor. After the blower is running, the fan can be placed back in the automatic mode at the thermostat.

If the blower runs but the burner does not come on, then you should check the reset button on the primary control. If the red reset button is sticking up, push it down and release it.

Is the side of the furnace warm to the touch?

If the burner still does not start, feel the side of the furnace. If the side of the furnace is warm, then check to make sure the air filter is clean. If the filter is clean, the problem may be the limit control.

If the side of the furnace is cool, the cad cell (flame sensor), the primary control or the burner motor may be bad. Some burner motors have a reset button on them.

Oil Furnace Troubleshooting, Got fuel oil?

If the burner motor starts but then stops and requires resetting the primary control, you should check that fuel is in the tank and that the fuel filter and nozzle are not plugged.

If you do not hear a sparking sound when the burner starts, the ignition transformer or the primary control may be bad.

Does the unit run but not put out enough heat?

After the burner ignites, the blower motor should start within 1-3 minutes. You should complete your oil furnace troubleshooting by observing a complete heating cycle.

When the home's temperature gets above the thermostat setpoint, the burner should shut off. The fan should continue to run for a few minutes to cool the unit. If it does not, the problem could be the fan/limit control or the fan timer control/relay.