Furnace after a winter power outage: restart steps and generator safety

By Jason Dearmin · Last reviewed November 14, 2026 · How we check facts

Restart steps for the furnace

1. Wait until power has been restored and stable.
2. Check that the furnace power switch (it looks like a light switch near the furnace) and the breaker are on.
3. Make sure the blower door is on and seated. Carrier notes that removing the blower door cuts 115 V to its control.
4. Set the thermostat to heat and a temperature above the room temperature, then wait a few minutes. Many furnaces start with a short pause and the inducer motor before igniting.
5. Check the thermostat display. Honeywell lists breaker, system power switch, a securely closed furnace door and the C wire as checks for a blank thermostat display.
6. If the LED shows a code, look it up for your brand.

It is normal for some furnaces to show a code or go into lockout after a power interruption, especially if the outage happened mid-cycle. Goodman says lockout can be reset by interrupting power, by waiting for the one-hour automatic reset, or by lowering the thermostat for a short time. If the furnace locks out again, call for service.

If you use a portable generator

The Washington State Department of Health gives these rules:

• Never use a portable generator in a garage, carport, basement, crawl space or other enclosed or partially enclosed area, even with ventilation. Opening doors and windows or using fans will not prevent CO buildup.
• Place the generator away from windows, doors and vents, at least 20 feet from buildings.
• Install battery-operated or battery-backup carbon monoxide alarms in the home and test them.
• Never plug a generator into a wall outlet (back feeding). It can electrocute utility workers or neighbors.
• The only safe way to connect a generator to house wiring is a power transfer switch installed by a qualified electrician.
• Keep the generator dry, let it cool before refueling, and store fuel in an approved container outside living areas.

Restarting a furnace after a power outage

1. Confirm power is stableWait until utility power is restored and steady.
2. Check the furnace switch and breakerMake sure both are on.
3. Check the blower doorIt must be installed and seated so the control has power.
4. Call for heat and waitSet the thermostat above room temperature and give the furnace a few minutes to start.
5. Look up any codeIf a code shows or the furnace locks out repeatedly, call a technician.

Frequently asked questions

How far should a generator be from the house?

The Washington State Department of Health says at least 20 feet from buildings and away from windows, doors and vents, and that you still need working CO alarms inside.

Can I plug my generator into a dryer outlet to run the furnace?

No. Washington DOH calls this back feeding and says it can electrocute utility workers or neighbors. A transfer switch installed by a qualified electrician is the only safe way to connect to house wiring.

Sources

• Generator Use During a Power Outage (Washington State Department of Health)
• Carbon Monoxide Safety (Washington State Department of Health)
• SP05-59 Service and Maintenance Procedures: Deluxe 4-Way Multipoise 2-Stage Direct-Vent Condensing Gas Furnace (Carrier (shareddocs.com)) Covers: Carrier 2-stage condensing gas furnaces with the status-code LED control described in the document. Other Carrier, Bryant and Payne boards can use different codes; check the service label on your furnace.
• RS6612023 Service and Troubleshooting: 34.5" Chassis ACVC96/AMVC96/GCVC96/GMVC96 Gas Furnaces (Goodman Manufacturing (Daikin)) Covers: Goodman and Amana 96% two-stage condensing furnaces in the 34.5" chassis.
• Troubleshooting and Support (T10 / T10+ Pro product data) (Honeywell Home (Resideo))

Safety note: this page is general information drawn from the sources above. Gas, combustion and line-voltage repairs belong to a licensed professional. Your own equipment's label and manual take priority over anything here. Read the full disclaimer.