Furnace Won't Start on the First Cold Night? Electrical Checks to Try First

Mid-October is when a lot of homeowners in Waukesha flip the thermostat to Heat for the first time since spring. Most of the time the furnace kicks on like it never left. Sometimes it doesn't, and the house just keeps getting colder.

A gas furnace still needs electricity to run. The thermostat, the control board, the igniter, and the blower motor all depend on power. That means a “dead” furnace is often an electrical problem, and some of the most common causes are things you can check yourself in a few minutes without opening up the equipment.

Start at the thermostat

Before you head to the basement, rule out the easy stuff:

• Make sure it's set to Heat, not Cool or Off, and that the set temperature is a few degrees above the room temperature.
• Check the batteries. Many thermostats run on AA or AAA batteries. A blank or dim screen is a strong hint.
• Check the schedule. A programmable or smart thermostat may still be following a summer schedule, or it may have lost its settings after a power blip.

ENERGY STAR, the federal energy-efficiency program, lists checking thermostat settings as one of the first items in a normal heating and cooling check-up.

Check the furnace power switch

Most furnaces have a dedicated on/off switch mounted on the wall or ceiling joist near the unit. It often looks just like a regular light switch, which is exactly why it gets turned off by accident. Someone storing boxes, reaching for a basement light, or doing summer projects can flip it without realizing what it controls.

If that switch is off, turn it on and give the furnace a few minutes. Many units go through a short startup sequence before the burner lights and the blower starts.

Check the breaker

Next, look at your electrical panel. Find the breaker labeled for the furnace. A tripped breaker usually sits in a middle position or is pushed toward off.

To reset it, push it fully to off, then back to on. Only do this once. If the breaker trips again right away or soon after, stop. A breaker that keeps tripping is telling you something is wrong, whether it's a failing blower motor, a short, or a wiring problem, and resetting it over and over can make things worse. That's a job for our electrical troubleshooting team.

If the panel has old, faded, or missing labels, this is a good reminder to get it labeled properly. It saves a lot of guessing on a cold night.

Make sure the front panel is seated

Many furnaces have a safety switch behind the front access door. If the door isn't fully closed and seated, the furnace won't run. If someone recently changed the filter, double-check that the panel went back on snugly.

Speaking of filters, ENERGY STAR recommends inspecting, cleaning, or changing the air filter once a month during heavy use. A badly clogged filter makes the system work harder and can lead to damage over time.

Signs to stop and call for help

Some symptoms go beyond a simple reset. Don't keep trying to restart the furnace if you notice:

• A burning or hot plastic smell near the furnace, the switch, or the panel.
• Scorch marks, buzzing, or a warm cover on the furnace switch, a nearby outlet, or the breaker.
• A breaker that trips again after one reset.
• Lights that dim or flicker when the blower turns on.
• The smell of gas. Leave the house right away and call your gas utility or 911 from outside.

ENERGY STAR notes that faulty electrical connections can cause unsafe operation of a heating and cooling system and shorten the life of major parts. That's why a normal pre-season check-up includes tightening electrical connections and checking motors.

Electrician or HVAC tech?

It depends on where the problem is. If the furnace itself has failed, such as the igniter, control board, or heat exchanger, that's HVAC work. If the problem is getting power to the furnace, an electrician is the right call. That includes a breaker that won't stay on, a damaged or overheating service switch, loose or burned wiring, or a panel that's showing its age.

In older homes around Waukesha County, we also see furnaces sharing a circuit with other loads or wired with connections that have loosened over decades. If you'd like a closer look at the whole system, our home electrical inspections cover the panel, circuits, and connections. If the panel itself is the weak link, see our panel upgrade service.

Get ahead of the first hard freeze

The best time to find a furnace problem is on a mild October afternoon, not at 2 a.m. in January. Turn the heat on now, listen for a normal startup, and walk through the checks above. While you're at it, make sure your smoke and CO alarms are working. Our electrical safety checklist covers the rest of the basics.

If your furnace won't stay on and you think the problem is electrical, contact Couillard Electric. We serve homeowners in Waukesha and across our service area.