A Quick Guide to Restarting Your Furnace

When your furnace suddenly stops working, it can leave your home feeling cold and uncomfortable. Restarting your furnace is often a quick fix to get the heat running again. With a few simple steps, you can have warm air blowing in no time.

Before restarting, it's important to understand why your furnace stopped working in the first place. Issues like a tripped breaker, clogged filter, or problem with the thermostat wiring can cause shutdowns. Taking the time to troubleshoot first prevents wasting effort on restarting when a larger issue is at play.

Check the Breaker and Reset if Tripped

One of the most common reasons a furnace stops working is a tripped circuit breaker. Locate the main breaker panel and look for the switch controlling the furnace - it likely will have a label. If the switch is halfway between ON and OFF, it's tripped. Carefully flip it all the way OFF and then ON again to reset it.

Avoid touching any wet surfaces while resetting the furnace breaker. Water and electricity don't mix! If the breaker trips again right after resetting, contact an electrician to inspect for shorts or overloaded circuits.

Signs of a Tripped Breaker:

• Furnace power light is off
• Blower not running
• Burners fail to ignite

Safety First When Resetting a Breaker

Taking proper safety precautions prevents electrical hazards like shocks or fires when resetting a furnace breaker:

• Make sure hands are completely dry before touching the breaker
• Stand to the side - don't stand directly in front when switching
• Only flip the switch once to reset - don't rapidly flip on/off
• If it trips again, shut off power and call an electrician

Wearing rubber-soled shoes and insulating gloves provide added protection when resetting an electrical breaker. Never reset a breaker while standing on wet surfaces or in water, which poses extreme electrocution risks.

If the furnace breaker trips repeatedly after resetting, a short circuit or overloaded wire is likely present. Continually resetting it without addressing the underlying issue can damage the furnace blower motor or other components. Contact a licensed electrician to inspect the electrical system.

Locating the Furnace Breaker

The furnace circuit breaker is normally located in the main electrical service panel, but may be in a subpanel in some homes. Check for labels indicating the furnace or air handler circuit. Typically, a 15-20 amp breaker controls 120v circuits for the furnace blower motor and thermostat transformer, while a larger 40-60 amp breaker supplies 240v to the heating elements.

If all breakers are unlabeled, turn them off one-by-one until the furnace stops running to identify the correct one. Shutting off the wrong breaker can cut power to other appliances, so take care in this trial-and-error process.

Resetting vs Replacing a Faulty Breaker

If a breaker trips due to a momentary power surge or overload, resetting it is fine. But breakers also wear out over time. A damaged breaker that frequently trips should be replaced. Signs that replacement is needed include:

• Breaker feels warm/hot to touch
• Reset button is difficult to push in
• Unexplained, frequent tripping occurs
• Scorch marks or burns on the breaker
• Buzzing, sizzling or humming sounds

Updating to a new breaker that matches the electrical specifications of the furnace prevents future issues. Consult the furnace manual or contact the manufacturer to confirm the appropriate breaker rating.

Examine the Furnace Filter

If your furnace burner ignites but shuts off after a few minutes, a clogged filter could be preventing proper airflow. Slide out the filter and hold it up to the light. If you can't see light passing through, it needs replacing. A dirty filter restricts air to the furnace burner, causing it to overheat and shut down.

Some filters have an arrow pointing in the direction of airflow. Make sure to install the new filter properly aligned to allow air to pass through unobstructed. Maintain your furnace filter by replacing it every 1-3 months to prevent clogging issues.

Signs of a Clogged Filter:

• Reduced airflow from vents
• Furnace cycling on/off frequently
• Burner flames appear smaller or weaker
• Unusual furnace noises or vibration

Selecting the Right Replacement Filter

Choosing the proper furnace filter type and size ensures optimal performance:

• Match the same size and thickness as original filter
• Use recommended filter rating by furnace manufacturer
• Choose electrostatic or pleated filters for better particle capture
• Avoid extremely dense filters that block airflow

The filter slot or owner's manual typically indicates the correct size and MERV rating. MERV measures a filter's particle retention - a higher MERV traps smaller particles. Balancing filtration with airflow is key - dense filters tax the blower motor.

Disposable fiberglass filters offer low efficiency at MERV 1-4. Pleated filters (MERV 7-13) trade longer life for better particle removal. Electrostatic filters (MERV 13-16) provide the best filtration using static charge to grab particles.

When to Change the Filter

Check filters monthly and replace per the manufacturer's suggested schedule. Expect to replace filters every 1-3 months for disposables, 3-6 months for pleated, and 6-12 months for electrostatic. Filter life also depends on use and contamination levels.

Signs your filter needs replaced:

• Decreased airflow at registers
• Dust, dirt, debris collecting on filter
• Furnace blower running excessively
• Reduced heating or A/C performance
• Strange smells from vents

A high-quality, properly fit filter changed regularly removes airborne particles that restrict airflow and damage furnace components.

Check Thermostat Settings and Wiring

Before hitting the reset button, ensure your thermostat settings are correct. Verify it's set to "heat" mode and the temperature is raised above the room temperature. Inspect the wiring connecting the thermostat to your furnace - loose wires or improper connections can prevent signals from passing between the devices.

Try rebooting the thermostat by removing it from the wall mounting plate, waiting 10-15 seconds, and reattaching it. This may reestablish communication if wires are properly connected. For dual fuel heat pumps, confirm the system switch is not stuck between heat/cool modes.

• Set target temperature higher than room temp
• Ensure wiring is securely connected
• Replace dead batteries if thermostat is battery powered
• Clean dirt/dust from thermostat screen
• Check for "C-wire" connection if a smart model

Carefully inspect the wiring connections on the furnace control board and at the thermostat. Loose wire nuts or pulled out wires can interrupt critical control signals. Wires labeled R, W, G, Y, and C correspond to specific thermostat functions.

Smart thermostats require a C or common wire for continuous power. Upgrading the wiring is recommended if this wire isn't present. A professional can also confirm your system is compatible with smart controls.