Safety first, always!

Stop and act right away if you notice any of these:

• You smell gas or rotten eggs. Leave the building, then call your gas utility or 911 from outside. Do not flip switches or use your phone inside.
• Your carbon monoxide alarm sounds. Get everyone outside and call 911.
• You see scorch marks, smell burning plastic, or see smoke near the furnace. Turn the furnace off at the breaker and call for service.

Everything below assumes none of those apply.

1. The thermostat is the problem

It sounds too simple, but a thermostat issue is one of the most common reasons a furnace seems dead.

What to check:

• Make sure the thermostat is set to Heat, not Cool or Off.
• Set the temperature at least five degrees above the current room temperature.
• Replace the batteries if the display is blank or dim.
• If you have a smart thermostat, check that it still has power and is not stuck in a schedule or away mode.

If the furnace starts after any of these, you are done. If not, move on.

2. A clogged or dirty air filter

A dirty filter restricts airflow. The furnace then runs hotter than it should, and its safety switch may shut it down before your home warms up.

What to check: Slide the filter out and hold it up to a light. If you cannot see light through it, replace it. Most standard filters need changing every one to three months during the heating season, and more often in homes with pets or heavy dust. Commercial spaces with high foot traffic may need to change filters more often.

A fresh filter is the cheapest fix on this list, and it also helps the system last longer.

3. Blown fuse or tripped breaker

Furnaces draw power for the blower motor, igniter, and control board. A power surge or an overloaded circuit can trip the breaker.

What to check: Find the breaker marked for the furnace and make sure it is fully on. Also check the service switch near the furnace, which looks like a regular light switch. If the breaker trips again right after you reset it, stop. That points to an electrical problem or a failing component, and repeated resets can make it worse.

4. A dirty or failed igniter or flame sensor

Modern gas furnaces use an electronic igniter to light the burners and a flame sensor to confirm the flame is lit. If the flame sensor is coated in residue, it can shut the furnace off a few seconds after it starts. If the igniter has cracked or worn out, the burners may never light.

What it looks like: The furnace tries to start, runs briefly, and shuts down. You may hear clicking or the blower starting, but no heat follows.

This is a common repair, and it is usually quick for a technician. We do not recommend opening the furnace cabinet yourself.

5. Blower motor or fan trouble

If the furnace is making heat but you do not feel warm air at the vents, the blower may be the issue. A failing blower motor, a worn belt, or a bad capacitor can leave the system running without moving air.

What it looks like: Weak airflow, rattling, squealing, or a burning smell from the blower area. The furnace may also run constantly without warming the space.

6. Closed vents, blocked returns, or duct problems

Sometimes the furnace is fine and the air is not reaching the rooms that need it.

What to check:

• Open any supply vents that are closed.
• Make sure furniture, rugs, or boxes are not blocking vents or return grilles.
• Feel the airflow at several vents. If one area is much weaker than the rest, there may be a duct leak or blockage.

Uneven heating in a building is also a sign to have the ductwork looked at, since leaks waste heated air before it reaches the room.

7. An Aging System 

Furnaces do not last forever. If yours is more than 15 years old and starts needing repairs more often, the repairs may begin to add up. A technician can look at the repair cost, the age of the unit, and your energy bills, and help you decide whether repair or replacement is the better choice. A good technician should explain both options, not push only one.

Repair or replace? A simple way to think about it

Ask these questions:

• How old is the furnace?
• How many repairs have you needed in the last two years?
• Is the heat uneven, or is the system running longer than it used to?
• Have your heating bills gone up without a change in usage?

If most answers point the wrong way, ask for a replacement estimate alongside the repair quote. Having both numbers makes the decision easier.

When to call Earl’s Heating

Call for service if:

• The furnace will not start after you check the thermostat, filter, and breaker.
• It starts, then shuts off again.
• You hear grinding, squealing, banging, or repeated clicking.
• The breaker trips more than once.
• Some rooms stay cold while others are fine.
• The furnace is old and has been repaired more than once recently.

Earl’s Heating provides heating service for both residential and commercial customers. Call us today or request service online, and we will help you get the heat back on.

Frequently Asked Questions About Furnace Repair

Q: Why is my furnace running but not blowing hot air?

A: A furnace that runs without producing heat often has an igniter, flame sensor, or gas supply problem. A dirty filter or a thermostat setting can also cause it. Start with the filter and thermostat, and call a technician if the problem continues.

Q: Why does my furnace keep turning on and off?

A: Short cycling usually comes from restricted airflow, a dirty flame sensor, or an overheating safety switch. A clogged filter is the most common cause and the easiest to check. If a new filter does not help, schedule a service visit.

Q: Is it safe to relight my furnace pilot light myself?

A: Many newer furnaces do not use a pilot light at all and light electronically. For older models, follow the manufacturer’s instructions exactly. If you smell gas at any point, leave the building and call your gas utility. When in doubt, call a technician.

Q: How often should I change my furnace filter?

A: Most standard filters need to be replaced every one to three months during the heating season. Homes with pets, allergies, or lots of dust, and busy commercial spaces, may need more frequent changes. Check your filter monthly and replace it when it looks dirty.

Q: How do I know if my furnace needs repair or replacement?

A: Age, repair history, and efficiency all matter. A furnace over 15 years old with frequent repairs and rising energy bills is a good candidate for a replacement estimate. A technician can compare the cost of repair against replacement for your situation.

Q: Do you repair furnaces in commercial buildings?

A: Yes. Earl’s Heating works on both residential and commercial heating systems. Call us with details about your building and equipment and we will schedule a visit.

Q: Does Earl’s Heating & Air Conditioning provide price estimates before the work begins? 

A: Yes. We provide the price of the work before we begin, with no surprises or hidden fees.

Earl’s Heating & Air — Northwest Indiana’s Commercial HVAC Specialists. Serving Lake, Porter, LaPorte, and Jasper Counties.