“Why Won’t My Furnace Turn On?” [FAQ]

There are several possible reasons why your furnace won’t turn on.

But we’re sure you’re just wondering, “Is there anything I can do to possibly fix this before calling a technician for help?”

Indeed there is!

Before scheduling with George Brazil for help, do these 4 things:

1. Check the thermostat settings
2. Ensure the furnace power switch is set to “on”
3. Check the furnace’s circuit breaker
4. Clear the condensate drain line

We’ll explain each of these in more detail.

Make sure that your thermostat is set to “heat.”

Furnace still isn’t on? Try turning the temperature 5 degrees above your room temperature.

Near your furnace is its power switch; It looks like this:

Because it looks like a light switch, someone may have flipped it off by mistake, turning off your furnace in the process.

Make sure the switch is flipped up (which usually means “on”).

Whether you have a gas or electric furnace, both use electricity to run the fan and therefore need a circuit breaker.

If the breaker “trips” (cuts flow of electricity), the furnace won’t turn on.

Go to the breaker (a grey metallic box or door usually found in a utility area) and see if the furnace’s breaker switch is in the middle position (meaning it tripped).

If it tripped, turn it to the “off” position (right) and then to the “on” position (left).

Breakers trip for a variety of reasons, like during a power outage. If the furnace breaker continues to trip, DON’T turn it back on. You have a more serious issue and need an electrician’s help.

If you have a high-efficiency furnace, the condensate drain line may have become clogged, causing water to back up and trigger an overflow shutoff switch.

So that’s why the furnace won’t turn on.

Let us explain.

A high efficiency furnace (90%+ AFUE) creates condensate that needs to be drained out of your home via a drain line. But if the drain line gets clogged with gunk (mold, slime, etc.), then that condensate goes back up the drain and into the furnace.

To avoid water damage, many furnaces have a switch that shuts off the furnace until the condensate drain problem is fixed.

How to clean the condensate drain line:

1. Find the main condensate drain near the furnace. It’s a vertical PVC pipe with an opening.
2. Use a wet-dry vacuum to suck out the gunk. Put the vacuum hose over the vertical opening and use your hand to make sure the hose is on the pipe airtight.
3. Pour in some bleach and hot water. If the above didn’t work, pour bleach into the main condensate drain. Wait 10-15 minutes and then pour in hot (not boiling) water. This should get rid of the mold and sludge.

If these 4 solutions didn’t work, contact a professional heating company!

And if you live in the Phoenix metro area, George Brazil Air Conditioning & Heating can help.

George Brazil Air Conditioning & Heating keeps Phoenix-area homes safe, comfortable and energy efficient. Contact us online for more information about any of our services.