Resetting a furnace after a power outage is the safe sequence of steps that clears a control-board lockout and lets the furnace try to fire again — and knowing when to stop and call a pro is part of it. Winter power outages in Fort Collins usually arrive with the weather that makes heat matter most: overnight lows in the teens and single digits from November through February, with about 150 freezing nights a year. When the power comes back and the furnace does not, the cause is usually simple — the furnace’s control board locked out during the outage, or a safety switch tripped — and the fix is a careful reset. The key word is careful. A furnace is a gas appliance, and the reset sequence below is the safe one. If anything smells wrong, skip straight to the bottom of this post.
Before you touch anything: safety first
If you smell gas, do not reset anything. Leave the house, and call the gas utility or a technician from outside. Do not flip switches, do not light anything, and do not go back in to check. The same applies if you see soot around the burner compartment, hear a repeated clicking without ignition, or your carbon monoxide detector has gone off. Those are not troubleshooting signals — they are stop signals.
Also check the obvious before you start: is the power actually back to the furnace? A tripped breaker is the most common post-outage fault of all. Furnaces run on a dedicated circuit, and the surge when power returns can trip it. If the breaker is tripped, reset it once. If it trips again immediately, stop — that is an electrical fault, not a reset problem.
The safe furnace reset sequence after a power outage
- Turn the thermostat to OFF and set the fan to AUTO. This stops the system calling for heat while you work.
- Turn off the furnace power switch — the wall switch beside the furnace, usually with a red cover — and then switch the furnace breaker off at the panel.
- Wait a full minute. The control board needs time to discharge and clear its lockout memory. Thirty seconds is the minimum; a full minute is safer.
- Check the filter and the furnace door. A filter packed with dust can trip the high-limit switch, and a blower-compartment door that is not firmly closed will trip the door safety switch and cut power to the burners. Replace a grey, matted filter and push the door firmly shut.
- Restore power: breaker on, then the furnace switch on. Wait for the inducer fan to start, then the igniter to glow, then the burners to light.
- Turn the thermostat back to HEAT and set it 3–5 degrees above room temperature. The burners should light within a minute or two, and warm air should reach the registers within five.
If the furnace lights and runs normally, you are done. Modern furnaces count failed ignition attempts — after three, the board locks out for one to three hours — so a single clean start after a reset is a good sign.
Fort Collins-specific wrinkles
Two local details catch people out. The first is altitude. Fort Collins sits at 5,003 feet, where gas furnaces derate about 12% because there is less oxygen per cubic foot of air, and a furnace that was never re-commissioned for altitude is more prone to ignition faults and lockouts — especially after a power interruption. If your furnace locks out more than once in a week, the underlying fault is still there and a reset will not fix it.
The second is the condensate drain. Modern condensing furnaces — which is what the 2026 ultra-low-NOx rule (HB23-1161, effective 1 January 2026) effectively requires — produce condensate that drains away through a small line. In a cold snap that line can freeze if it runs through an unheated space, and a frozen drain trips a safety switch that shuts the furnace down. If your furnace died during a cold night after an outage, check whether the condensate line is frozen before you assume the worst. Do not use a torch or an open flame on it; warm water or a hair dryer on low, applied gently, is the safe approach — and if you are unsure, call a technician.
When to stop and call a technician
Stop resetting and call for furnace repair if the furnace locks out again within a day, if you smell gas, see soot, hear clicking without ignition, see a yellow or orange flame instead of a steady blue one, or if the breaker trips again after you reset it. Also call if the air is cold at every register — that points to the burner compartment or the ductwork, not the thermostat. Repeatedly cycling a furnace that will not light dumps unburned gas into the heat exchanger, so two failed attempts is the limit for a homeowner. A technician will check the flame sensor, the igniter, gas pressure at the valve and the control board — and if your system is due for its annual service, a furnace maintenance visit covers the same ground before the next outage. For a no-heat situation at night, our emergency HVAC repair page explains what to expect when you call after hours.
Get help with HVAC in Fort Collins
If the reset worked and the furnace is heating normally, you are done. If it locked out again, or anything in the list below applies, call DNA Refrigeration Heating & Cooling for furnace repair in Fort Collins — (970) 932-2324. We are open 24 hours, 7 days a week.