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Why Isn't My Furnace Kicking On?

If your furnace doesn’t kick on when your house is cold, it can be the worst feeling! Nights get cold in Missouri and coming home to a freezing house is no fun. There are many reasons that can cause furnace failure! The trick is finding out the source of the problem. Here are a few reasons why your furnace may not be working:

Furnace Tune Up by No Problem Heating and Cooling

The Most Common Furnace Problem

Jay over at Word of Advice TV goes over the most common furnace problem and how to fix it. (Hint: it’s the flame sensor.) And it’s exactly the reason that regular furnace maintenance is so important. Dust, debris, and carbon build up up over the months. This video is primarily for folks who are hands on or for those who are just interested in the specifics of how things work. The professional HVAC technicians at No Problem Heating & Cooling are happy to do this type of repair and maintenance safely for you.

General Furnace Check List

Your furnace might not be kicking on or it is kicking on and off. The blower runs constantly or is just not heating. Review this check list of common issues you might experience with almost any furnace (electric or gas). These are things most homeowners can do before calling on their HVAC professionals.

Power Problems

First, find out if you have gas or electric furnace. You need electric power for both for the furnace to kick on. Check the circuit box and around the unit to see if any hungry critters have been nibbling on your wires.


One of the easiest ways to troubleshoot a furnace malfunction is to check your fuses first. If you have a blown or loose fuse you will not have power at all. You have to remember these machines are so easy but so hard to work on. Buy a new fuse and replace it with the same amp.

Loose Wires

Vibration can cause wires to come loose. At some point, all of the vibrations will rattle wires. When you have your inspection done each year, your HVAC professional will check all of the connections and make sure nothing is loose.

Blower Motor

Most blower motors have an inspection window on the furnace. The flashing green light lets you know everything is okay. If you see a red light, it means your furnace is having problems. When your contractor comes out, they will inspect the control board, motor, and transformer.


Be sure to check your thermostat. Many of the new digital thermostats have fail-safes and different modes that could cause the furnace not to start.

Check the thermostat and make sure it’s set to heat. If it’s 40 degrees outside and you have it set to 38, it won’t kick on. The temperature to heat should be set to higher than the actual temperature in the house.

Also, if the thermostat has been switched to fan please change it to heating. This is a very commonly forgotten step.

Air Filter

One of my favorite furnace issues because it is the cheapest for you is the dirty old air filter. You have to be aware of and maintain your air filter. The changing of an air filter can take less than a minute. If you are into NASCAR, even faster than that. Remember keeping that air filter clean can save hundreds of dollars over the life of the furnace.


A condensation pan on the furnace collects excess water and if this gets full, it will cause the furnace to stop turning on. Normally, draining of the pan is not an option although it could work temporarily. We have seen blockages that prevented water from draining. In addition, we have seen a bad condensation removal pump.

Starting Capacitor

Sometimes a starting capacitor is not giving enough power to the system to kick it on. Fortunately, replacing your capacitor is an easy and cheap fix.

Check List for Gas Furnace Repair

Review this check list of common issues you might experience with your gas furnace.

Gas Supply

Check your gas valve and make sure nothing is off. Some homeowners turn down the valve during the summer months or it may have been switched accidentally at some point.

Not Enough Gas

Take the time to check the valve is completely on. Sometimes, a furnace won’t kick on because the valve is half turned.

Gas Valve

You could easily have a failing gas valve in your lines. When debris gets in the valve, it can make it hard for it to open or close. When this happens, it will heat up then the system will short and blow a fuse.

Pilot Light

Check for your pilot light – it should be blue. If you don’t see it, make sure you call an expert.

Electric Furnace Repair

Your electric furnace is going to be much different from the gas furnace check list. The control board is going to be your main source of power. Unless you know what you are doing, we would not recommend messing with it. Call your local HVAC contractor, like No Problem Heating & Cooling, to have it inspected and fixed.

HVAC Maintenance Program

HVAC Pro Tip: Having a maintenance program agreement with an experienced HVAC company can prevent this entire scenario from happening. 

Furnace issues often appear when the first chill sets in. While we wish those warm days are going to last forever, we forget just how cold winters can be! Meanwhile, your furnace has been inactive for half a year. As a Club Member, you’re shielded from these surprises. We’ve got you covered, no matter the make or model of your furnace.

Every Club Membership includes two visits per year. We come once in the fall to inspect and maintain your furnace and once in the spring for your air conditioning unit. Learn more and sign up for our Club Membership today.

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Areas We Serve

Proudly installing, repairing, and maintaining all types of residential and commercial HVAC systems in St Charles and the St Louis Metro Areas.

  • St Charles County, Missouri
  • St Louis County, Missouri
  • Warren County, Missouri
  • Franklin County, Missouri

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