Furnace Won't Start? What to Check Before You Call

When the house is cold and the furnace won't kick on, the first instinct is to call for help right away, and sometimes that is the right call. But a good number of no-heat calls trace back to something a homeowner can safely check in five minutes: a thermostat setting, a tripped breaker, a filter that has not been changed in a while. Working through a short list before you pick up the phone can save you a wasted trip, or at least tell the electrician what to expect when they arrive.

Start with the thermostat

It sounds obvious, but thermostat problems are more common than people expect. Confirm the thermostat is set to Heat, not Cool or Off, and that the set temperature is a few degrees above the current room temperature. If the display is blank or dim, the batteries may be dead, which on some systems is enough to stop the furnace from firing even though the rest of the house has power. Replace the batteries and give the system a minute to reset. If the thermostat is hardwired and still blank, that points toward a power problem rather than the thermostat itself, and that is worth noting before you call.

Check the breaker and the furnace switch

Furnaces run on electricity even when they burn gas or propane, so a tripped breaker will stop them cold. Find your electrical panel and look for a breaker sitting in the middle rather than fully on, or a switch labeled for the furnace or air handler. Switch it fully off, then fully on, once. If it trips again immediately, stop. That is not a fix-it-yourself situation, it is a sign something downstream is drawing too much current, and resetting it over and over is a real safety risk. Also check for a toggle switch near the furnace itself, sometimes mounted on the unit or on a nearby wall or ceiling joist, that gets bumped off by accident.

• Panel breaker: look for one sitting in the middle, not fully on
• Furnace switch: a wall or unit-mounted toggle that looks like a light switch
• Reset once; if it trips again, stop and call rather than resetting repeatedly

Look at the filter

A badly clogged filter can choke off airflow enough that some furnaces shut themselves down as a safety measure. Pull the filter and hold it up to a light. If you cannot see light through it, it needs to be replaced. This is one of the few checks that doubles as routine maintenance rather than troubleshooting, since a dirty filter also makes any furnace work harder and shortens its life. If you are not sure where your filter lives, it is usually in a slot near the return air duct or built into the furnace cabinet itself.

Signs of a flame or ignition problem

If the blower runs and air is moving through the vents but no heat ever shows up, that points toward the burner or ignition side rather than the electrical side. A furnace that clicks repeatedly, tries to light, and then shuts off is often struggling with a flame sensor or igniter that is dirty or wearing out. These are not something to test yourself. The gas or propane side of a furnace is not a do-it-yourself repair, and opening the burner compartment without the right training is a real hazard.

• Repeated clicking with no flame that catches
• A burning smell that does not fade after a few minutes of running
• Short cycling: the furnace runs briefly, then shuts off again and again

When to stop and call

Any burning smell that lingers, any breaker that trips more than once, or any sign of scorching or soot near the furnace means it is time to shut the system off at the breaker and call rather than keep troubleshooting. The same goes for anything involving the gas line, the flame sensor, or the inside of the burner compartment. The checks above handle the simple causes. Everything past that point is electrical or combustion work that should go to someone trained to be inside a furnace cabinet safely.

If you have gone through this list and the furnace still will not start, Dan's Electric Shop & Electro Electric handles furnace and heating calls across Noble and the surrounding Richland, Clay, Jasper and Wayne county area, with a 24-hour weekend emergency line at 618-723-2515 and free estimates on repair or replacement.