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Why Won’t My Furnace Turn On?


When you switch your thermostat to “on,” only to find that you don’t get any warm air flowing through your home, your first response may be to call the HVAC professionals. While the team at Black Diamond is happy to help, we want you to know that you may be able to fix the problem on your own and save the cost of a service call.

Here are some steps to take to troubleshoot the problem before you call our team.

1. Check for PowerTechnician servicing a furnace

Is there power running to the furnace? Obviously, check the electrical connection, but also check the circuit breaker. If the circuit breaker has switched to the “off” position, reset them, and try to start the furnace again. If the breaker trips again, then you need a professional to take a look at it.

Don’t tape the circuit breaker into the “on” position or reset it more than once, because doing so puts your home at risk for an electrical fire. If resetting it once doesn’t help, call Black Diamond.

2. Check the Thermostat

It may seem obvious, but if your furnace isn’t turning on, check the thermostat. Our team has gone to many service calls only to find that the thermostat was low on batteries or lost power. Make sure the thermostat has power running to it, is in the “on” setting, and is set to “heat” and not cool. Also, bump up the temperature about 10 degrees to make sure the furnace is really not turning on.

3. Check the Air Filter

Some furnaces are designed to turn off if the air filter is clogged. This is a safety measure to prevent the furnace from overheating. If your furnace won’t switch on, check the air filter and change it if needed.

4. Check the Condensate Pan

When the air conditioner runs, it will accumulate water in the condensate pan. When operating as it should, the pan will drain or be pumped out of your home. However, sometimes the drain or pump gets clogged, and the pan fills with water. This triggers a float switch, which prevents the furnace from running. Once you address the clog, your furnace should switch on.

5. Check the Pilot Light

Sometimes the pilot light in a furnace will go out. In this case, the furnace won’t turn on or heat properly. Not all modern furnaces have pilot lights, but if yours does, check to make sure it’s lit. Relight it, and try turning on the furnace again.

6. Check the Propane or Gas Supply

If all of the above check out, make sure your gas service is running properly. To do this, try lighting your gas stove or running your gas dryer. If those won’t start either, call the gas company.

7. Check the Ignition Sensor

Finally, if all else fails, consider checking the ignition sensor. This isn’t a task for the average homeowner, but if you’re pretty skilled with DIY tasks, you can do this. If the sensor is dirty, consider cleaning it and trying to start the furnace.

8. Call the Pros at Black Diamond Plumbing & Mechanical

If you’ve done the above steps and your furnace still won’t light, it’s time to call the pros. Black Diamond Plumbing & Mechanical has 24/7 service for Chicago-area homeowners and business owners.

Call us to schedule a service and find the root cause of your furnace problems.

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