Ways to Keep Your Furnace Functioning

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Home improvement

Maintaining Oil Furnaces: Controls and Stack Maintenance

An employee at a heating oil refueling station in Ruesselsheim near Frankfurt, Germany, is fixing a filler for a residential heating system.
Ralph Orlowski/Getty Images

Many oil furnaces have two primary switches, with one located close to the burner unit and the other near the furnace housing or further away from the furnace. Ensure that both of these primary switches are turned ON.

The stack control of the oil furnace, which is situated in the stack, is a safety device that monitors the oil burner’s operation. The stack control shuts off the motor if the burner fails to ignite. However, more often than not, a furnace shutdown is caused by a malfunctioning stack control rather than by the burner.

If the burner fails to ignite, check the fuel tank first and refill it if necessary. If the tank doesn’t require refilling, press the reset button on the stack control. If the burner still doesn’t ignite after pressing the button once, clean the control as outlined below. Then, press the reset button again. If the burner still doesn’t operate, call a professional service person.

The stack control gradually collects soot during the heating season, which can cause it to malfunction. To keep it operating correctly, clean the control every month or as soon as it becomes covered in soot. Here’s how to clean the stack control:

Step 1: Remove the bolts that secure the control in the stack. Pull out the sensor and its housing.

Step 2: Use a brush dipped in soapy water to remove all of the soot from the control. Wipe the control dry with a soft cloth.

Step 3: Before putting the control back in place, clean the stack. Spread newspaper on the floor to safeguard it, then dismantle the stack. As you work, remove the soot and debris from each section by banging them firmly on the newspaper-covered floor.

Step 4: After cleaning each section, reassemble them in reverse order. Ensure that the stack sections are correctly aligned and firmly connected.

Step 5: Lastly, reposition the stack control in the stack, and reseal the connection to the 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 on. If the burner still doesn’t ignite, or if it is very dirty, call a professional service person.


1. What are some signs that my furnace needs maintenance?

If you notice that your furnace is making unusual noises, producing odors, or not heating your home as effectively as it used to, it may be time for maintenance. Additionally, if your energy bills are higher than usual, your furnace may not be running as efficiently as it should be, indicating a need for maintenance.

2. How often should I have my furnace serviced?

It is recommended to have your furnace serviced annually by a professional HVAC technician. This will ensure that your furnace is running efficiently and prevent any potential safety hazards.

3. Can I perform maintenance on my furnace myself?

While there are some basic maintenance tasks that homeowners can perform themselves, such as changing the air filter, it is recommended to have a professional perform more complex maintenance tasks. Attempting to perform these tasks yourself could result in damage to your furnace or injury to yourself.

4. What should I expect during a professional furnace maintenance appointment?

A professional technician will typically inspect and clean various components of your furnace, including the burner, blower, and heat exchanger. They will also check for any potential safety hazards and ensure that your furnace is running efficiently. Additionally, they may recommend any necessary repairs or upgrades.

5. How can I prolong the lifespan of my furnace?

Regular maintenance is key to prolonging the lifespan of your furnace. Additionally, ensuring that your furnace is properly sized for your home, using high-quality air filters, and keeping your air vents unobstructed can all help to keep your furnace running efficiently and extend its lifespan.

6. What should I do if my furnace stops working?

If your furnace stops working, first check that your thermostat is set correctly and that the circuit breaker hasn’t tripped. If these do not seem to be the issue, contact a professional HVAC technician to diagnose and repair the problem.

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