Four checks resolve a large share of no-heat calls, and none of them require tools. Thermostat, breaker, filter, and door panel — in that order.

Check the Thermostat First

It sounds obvious and it is genuinely the most common cause.

Confirm it is set to HEAT rather than COOL or OFF. Confirm the setpoint is above the current room temperature — a thermostat set to 68 in a 70 degree house will not call for heat.

Check the batteries if it uses them. A dying battery produces erratic behaviour before it produces a blank screen.

If it is a programmable model, check whether a schedule is overriding what you set. Schedules survive power outages on some models and reset on others, and after a long outage a thermostat may be running a program nobody chose.

Check the Breaker and Switch

Find the breaker for the furnace and confirm it has not tripped. A tripped breaker is not always visually obvious — flip it fully off, then back on.

Also look for the furnace service switch. It usually looks exactly like an ordinary light switch, mounted on or near the unit, and it gets flipped by accident with remarkable regularity — particularly in garages and utility rooms where people reach for a light.

Check the Filter

A severely clogged air filter restricts airflow enough that the furnace overheats and shuts down on its high-limit switch.

The pattern is distinctive: the furnace runs for a few minutes, then shuts off before reaching the setpoint, then tries again later. If that is what yours is doing, look at the filter before anything else.

Replace it if it is dirty. This resolves more service calls than any other single check.

Check the Door Panel

Most furnaces have a safety switch that prevents operation unless the blower compartment door is fully seated.

If anyone has been near the furnace recently — changing a filter, retrieving something from storage — a panel that is closed but not latched will keep the system off entirely. Push it firmly into place.

Check the Gas

If other gas appliances in the house are also not working, the problem is the gas supply rather than the furnace.

On propane, check the tank level. It is a more frequent cause than homeowners expect, particularly during a cold snap when consumption is higher than usual.

Check the Vent Outside

Look at the exhaust termination on the exterior of the house. Nests, debris, ice, or damage will block venting, and the furnace will lock out on a safety rather than run.

This is worth checking after any storm.

Look for a Fault Code

Most modern furnaces have a small window on the control board with a blinking LED. That blink pattern is a diagnostic code, and the legend is usually printed inside the door panel.

Write down what it is doing before you cycle the power. Resetting clears the code, and intermittent faults are the hardest ones to catch on a service call. A homeowner who says “three blinks, about twice a week, usually in the morning” has saved real diagnostic time.

Stop Here

Beyond these checks, furnace work involves gas, high-temperature combustion, and electrical components that hold a charge after power is removed.

Do not open the burner compartment, adjust the gas valve, or bypass a safety switch. Those safeties exist because the failure modes are serious.

Call Immediately If

You smell gas — leave the house and call from outside. A CO alarm sounds. There is a persistent burning smell, visible soot, or loud banging at ignition.

During a hard freeze, no heat also puts your plumbing at risk, which makes it more urgent than the temperature alone suggests.

If the Checks Do Not Fix It

Common causes beyond homeowner reach are a failed igniter, a dirty flame sensor, a pressure switch fault, or a blower capacitor. All are routine furnace repair items.

Annual furnace maintenance catches most of them in advance, and emergency heating repair is available around the clock.

Contact 72 Degrees or call (830) 240-1835.