Furnace not Blowing Hot Air? Here’s what Might be Going on

If your furnace won’t turn on or is not blowing hot air, it could mean several things — some simple, some more serious. Here’s a quick guide:

1. Thermostat issues

You’d be surprised how many of our customers don’t check their thermostats before calling. The first thing to check is the fan setting. If it’s set to “on,” it’ll continue blowing at all hours. Switch it from “on” to “auto.”

In most cases, flipping the switch will make your furnace heat your house again. If it doesn’t, look at the temperature setting. Is it set to higher than the current temperature in your house?

If you live with other people, they might be fiddling with the temperature settings. It’s always a good idea to check the setting.

If there’s no difference after changing the temperature, or you see that the setting’s already higher than the current temps, you can try one more thing: Check the batteries and replace them.

Still no luck? You might need to have your thermostat recalibrated or replaced.

2. Dirty air filter

It may seem like the technicians at Jansen Heating & Cooling are broken records when it comes to keeping furnace air filters fresh, but an astounding number of problems really do come down to a dirty filter!

Changing your filters regularly is the best thing you can do to keep your HVAC system running as cost-efficiently as possible for as long as possible (and getting your spring and fall tune-ups done of course!)

• A clogged filter restricts airflow and can cause the furnace to overheat and shut off the burners as a safety measure.
• The fan will keep running, but no hot air will come out.

3. Pilot light or ignition failure (Gas furnaces only)

• Older units: Your pilot light could be out.
• Newer units: Your electronic igniter could fail.
• No flame equals no heat being produced.

4. Faulty flame sensor

• If the flame sensor is dirty or malfunctioning, the system may light briefly, then shut off, blowing cold air afterward.

5. Overheating/limit switch triggered

• A safety mechanism turns off the burners if the unit overheats (due to dirty coils, blower problems or airflow blockage).

6. Gas supply issues

• No or low gas supply to the furnace will prevent it from working properly.
• Check if your other gas appliances (like your stove or water heater) are working. If they are, the problem is probably not gas supply.

7. Ductwork problems

• Leaky or disconnected ducts can allow warm air to escape before it reaches your rooms.
• If this is the issue, you will feel only cold or lukewarm air coming from the vents.

8. Blower motor problems

• If the motor is malfunctioning, it may not circulate the heated air properly.

When to call a pro

If you’ve checked simple things (like the thermostat and filter) and the issue continues, if you hear strange sounds like banging or squealing, or if you smell gas, it may be time to call a Cincinnati heater repair company like Jansen.

In the third instance, if you smell gas, turn off your furnace immediately and give your utility company a call first; then call us.

Here are some quick do-it-yourself checks you can do before calling a Cincinnati furnace repair firm:

• Set the thermostat to “HEAT” and “AUTO”.
• Check/change the air filter.
• Turn the power off and back on.
• Confirm the pilot light is lit.

Never hesitate to call if you think there may be a problem.