If your furnace is dead and the house is getting cold, start with the thermostat, the furnace switch, the filter, and the breaker. Those four account for a lot of the no-heat calls we run, and all four are things you can check in about five minutes without tools. If none of them is the problem, it is time to call somebody, because the next layer down involves gas and high voltage.
Check these four first
The thermostat. Set it to HEAT and push the target temperature five degrees above where the room actually is. A thermostat set to 68 in a 68 degree room has no reason to call for heat. If the screen is blank, it is usually batteries. Most models take two AAs behind the faceplate.
The switch on the furnace. There is a light switch on or near the furnace itself, and it looks exactly like a regular wall switch. People flip it off while carrying laundry past it and never notice. Make sure it is on.
The filter. Pull it out and hold it up to a light. If you cannot see light through it, that is your problem. A clogged filter chokes the airflow, the heat exchanger overheats, and the limit switch shuts the furnace down to protect itself. This is the single most common thing we find, and it is the one that costs you nothing to fix.
The breaker. Find the furnace circuit in your panel. If it has tripped, push it fully OFF and then back ON. If it trips again right away, stop. Something is drawing current it should not be, and resetting it repeatedly is how small electrical problems become fires.
Then check the door
Furnaces have a safety switch on the blower door that cuts power when the panel is off. If somebody had the cover off recently, it may not be seated. Push it firmly until it clicks.
What we look at when we get there
Past that point you are into the sequence of operation, and that is where a meter and some experience start to matter.
We watch the furnace try to start and see how far it gets. That alone narrows it down fast. A unit that never even hums has a control power or board problem. One that starts the inducer motor but never lights has a pressure switch, an igniter, or a gas supply issue. One that lights and then shuts down after a minute or two is almost always overheating or losing its flame signal, which points at airflow or a dirty flame sensor.
Then we check the things that are genuinely unsafe to guess at: gas pressure, the heat exchanger, and the flue. A cracked heat exchanger is the reason we red-tag a furnace and shut it off rather than patching around it. That is a carbon monoxide risk and it is not something to nurse through a cold snap.
The lake-effect wrinkle
Northwest Indiana adds one failure mode a lot of general troubleshooting guides miss.
High-efficiency furnaces vent through PVC pipe out the side of the house instead of up a chimney. During a heavy lake-effect band coming off Lake Michigan, snow drifts against the side of the house and buries those pipes, or the exhaust condenses and freezes into a plug at the pipe opening. The pressure switch senses the blockage and locks the furnace out. It is doing its job.
If you get a no-heat call the morning after a big band comes through Hobart, Portage, or anywhere along the lakeshore, go outside and look at the two white pipes coming out of your wall. If they are packed with snow or capped with ice, clear them carefully by hand and give the furnace a reset. Do not use anything sharp and do not pour hot water into the pipe. Then keep an eye on that spot the rest of the winter, because whatever drifted there once will drift there again.
When to stop and call
Call us if you smell gas, if the breaker trips more than once, if the furnace lights and then quits repeatedly, or if you have a carbon monoxide alarm going off. That last one means leave the house first and call from outside.
We run heat calls around the clock in Lake and Porter County, including nights and weekends, because a furnace that quits at 2am in February is not a problem that waits until Monday.
Furnace repair and installation is what we do. If you are staring at a cold furnace right now, call and we will talk through it.
Want somebody to just look at it?
We cover Lake and Porter County, and we answer the phone around the clock for emergencies. Licensed, bonded and insured.