Many homeowners face problems like furnaces not turning on or blowing cold air. It seems more painful when you are shivering on a cold winter night and now your last ray of hope is gone.

You might think that what’s the use of a furnace if it doesn’t work when needed? And then replace it with a new one. But most of the problems with the furnace are normal issues. With proper inspection, sometimes you can find them yourself and fix them. But if it seems like a gas or electricity problem, never try to fix it. Calling a professional always helps.

Now, in this article, we will discuss the causes of furnaces not turning on or blowing cold air. Here are some reasons.


If you feel your furnace blowing cold air, it might be due to issues with the thermostat. First, see if the thermostat is switched to the heating function. After that, ensure the temperature is set lower than the temperature in the home. Sometimes, the thermostat itself is wicked. This problem requires professional attention.


If you haven’t changed your air filter in quite a long time, replace it quickly. It may be the solution to your current furnace problem. A dirty air filter is the most common cause of blowing cold air from your furnace. When your air filter is clogged, it causes overheating by blocking airflow over the heat exchanger. For this, the heat exchanger is shut off because your furnace may trip to a high limit. It is recommended that the air filter be changed every 90 days.

Pilot Light

Faulty pilot light or ignition sensor is the most common issue when a furnace is blowing cold air. When the furnace doesn’t fire up, even if you can hear the clicking. Then the problem is the pilot light.

Sometimes you will see the pilot light is lit, but it’s burning with a weak yellow flame. This signals that the pilot light is dirty. It needs to be cleaned properly for it to function properly.

You may also face problems with the thermocouple, meaning the components need to be replaced or adjusted. This type of work is technical, don’t try to do it yourself. Call a professional.

Gas Line

A disrupted gas supply to the furnace might be another reason for the furnace not turning on.

Examine the shut-off valve to verify that the gas is turned on. If it’s okay; after that, check other appliances that use the gas line. If they are working properly, in that case, your furnace’s gas line might be damaged. Check that the line is open and clear. Hire a professional to inspect and repair the problems with the gas line because it’s risky to do it yourself.

Power Line

You use different kinds of fuel to power your furnace. However, it needs electricity too.

Sometimes the problem with the power line is simple. Many forget to plug the power cord into the furnace. If it’s plugged in, then check the circuit box. However, if you see any burn marks on control boards, this may have been caused by an electrical short. Never try to solve a critical electrical problem without an expert’s help.

Dirty Flame Sensor

The flame sensor is a safety device. It tells the furnace controller if there’s a flame in the furnace. On the condition that there’s no flame inside the furnace, it signals to shut off the gas valve. In this way, it prevents your furnace from becoming a live bomb. When the flame sensor becomes dirty, it will lose its ability to detect whether or not the burner is turned on. Sometimes it will halt them from igniting at all. This results in cold air blowing out of the furnace.

Breaker Problems

If your furnace is electric, a tripped breaker will cause problems like the improper circulation of heat throughout the home. In the case of a gas furnace, it will make the furnace blow out cold air. Because an electric starter may have been used to ignite the gas burner. So if you see problems with your furnace, checking out your electrical panel is a good way to start.

Other Minor Causes

  1. Large holes and leaks in your air ducts will cause cold air to get into your crawlspace or attic. It will look like your heating isn’t working.
  2. “Short cycling” means when the furnace is turned on but turns off quickly. Airflow problems and the building of dust and grime within the furnace cause it.

If any of the access panels are not properly settled, a built-in safety feature (installed in the recent or new furnace) will turn off the furnace. So make sure that any of your panels don’t have any missing crews, or have popped out of place, or are open for other reasons.

Quick Tips to prevent furnace problems

Regular checking out is the best way to avoid problems. Every appliance needs proper maintenance. Do these following steps, before problems cut a big slice from your monthly budget.

  1. Replace the filter at least every 90 days. At a minimum, try to replace them once a season.
  2. Before each winter, ensure that all furnace-related appliances (pipes, humidifiers, air cleaners, etc.) are in good working order.
  3. Make sure there isn’t any water leakage.

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