3 Most Common Furnace Problems & Solutions in Colorado

November 13, 2020

A malfunctioning furnace can create inhabitable living conditions during the cold Colorado winters. Unfortunately, furnace issues can pop up at any time. However, understanding the symptoms and common furnace issues you might encounter can help you spot issues quickly (and save you money).

In Colorado, the most common furnace problems you’ll face are: 

  1. A furnace that’s blowing cold air
  2. A furnace that won’t turn on
  3. A grinding noise coming from your furnace

In this blog, we explain what causes these problems and which ones you can fix yourself. 


Rather have a Colorado pro look at your furnace ASAP? Contact the Cooper Green Team. We provide fast, 24/7 furnace repairs in the Denver and Colorado Springs areas. We’ll get your furnace up and running in no time.

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Common problem #1: Furnace blowing cold air

There are several different reasons your furnace may be blowing cold air. A furnace that blows cold air could be a result of an improper thermostat setting, a dirty air filter, a faulty fan limit switch, or something else entirely. 

To figure out what’s causing the cold air, you need to determine when cold air is blowing. 

  • Does it happen immediately after starting and then eventually the air warms up? 
  • Does it blow cold air sometimes and warm air other times?
  • Does it consistently blow cold air?

Let’s discuss the different causes and solutions for each of these situations….

A furnace that blows cold air immediately but eventually warms up

The most common cause of a furnace that blows cold air before warming up is a faulty fan limit switch

Your furnace has a fan that pulls in cold air and pushes out warm air. After the heat exchanger (which is the part that warms the air)  has heated up, the fan limit switch signals the fan to switch on. If the fan limit switch malfunctions, it may turn on the fan too soon and circulate cold air through your home before the heat exchanger heats up.

Do this: Call a HVAC technician, who will test the fan limit switch and replace it if necessary. 

A furnace that blows cold air and warm air intermittently

Possible cause #1: Improper thermostat setting

The most common cause of a furnace that blows cold and warm air intermittently is a thermostat fan setting that is set to ON.

Furnaces run in heating cycles and only produce hot air for short bursts of time. When your fan setting on your thermostat is set to AUTO, the fan only blows when the furnace is heating the air.

If your thermostat is set to ON instead of AUTO, the blower motor will run constantly, even when the furnace isn’t actively heating the air. 

An improper thermostat setting is an easy problem to solve.

Do this: Check your thermostat setting. If it is set to ON, switch it to AUTO. 

Possible cause #2: Furnace overheating 

If your thermostat is set to AUTO and your furnace is blowing hot and cold air intermittently, your furnace is most likely overheating.

As we mentioned earlier, a fan in your furnace pulls in cold air and pushes out warm air. During normal operation, a heat exchanger heats up cold air from inside your home. The blower then blows warm air into your home. 

When a furnace overheats, a safety switch shuts off the heat exchanger and the fan continues to blow to cool it down. As the heat exchanger is cooling down, you may feel cool air coming from your vents. 

Why is your furnace overheating? Lack of airflow is the most common cause of an overheating furnace. When there is an insufficient amount of cool air blowing over the hot heat exchanger, the temperature of the heat exchanger will rise. When it reaches unsafe temperatures, a safety feature triggers the furnace to shut down the gas burners that heat the heat exchanger.   

Low airflow in a furnace is caused by:

  • DIrty air filters. Air filters prevent dirt, dust and other contaminants from clogging the ventilation system. However, an air filter that is clogged with dust restricts airflow to the furnace.  Be sure to check your air filter monthly and replace it if it’s dirty. 
  • Dirty components. If your air filter is clogged with dirt, there’s a good chance that the furnace components are also dirty. Dirty components (clogged ducts, dirty fan blades, dirty blower motor, etc.) restrict airflow to the heat exchanger and can also cause the motors driving the furnace components to overwork and eventually overheat, all of which can eventually lead to mechanical failure. 
  • Closed or blocked vents. To make sure airflow to your furnace is unrestricted, keep the vents throughout your home open (even in rooms you don’t use) and unobstructed by furniture or other items. 
  • Mechanical failure. Regular use will eventually wear down an older furnace, especially if it’s dirty. That’s why it’s important to have an HVAC technician inspect and clean your furnace annually.

Do this: If you suspect your furnace is overheating, you will need to check your air filter and replace it if it’s dirty. Open any closed vents and remove obstructions from blocked vents. 

If your air filter is clean and your vents are open and unobstructed, contact an HVAC technician to diagnose your problem. 

A furnace that consistently blows cold air

It can be frustrating to have a furnace that is blowing cold air and never warms up, but don’t worry. This is most likely an easy fix. 

Possible cause #1: An improper thermostat setting is the most common cause of a 

furnace that consistently blows cold air with a strong/normal airflow.  

This is a common mistake homeowners make when the seasons change. If the homeowner hasn’t switched the thermostat to heat or raised the desired temperature of the home, the HVAC system may actually be triggered to cool the home and blow cool air (depending on the outdoor temperature and the set temperature on the thermostat).

Do this: If your thermostat is set to COOL, switch it to HEAT. 

Possible cause #2: If you’re getting weak but cool airflow from your furnace and your thermostat is set to HEAT, you may have leaky ducts.

It’s not uncommon for some warm air from the furnace to escape from the ducts into unheated areas of the home like the attic. However, if you feel a weak airflow that feels colder than it should coming from your furnace, you could have a major leak in your ductwork. 

When heated air from the furnace leaks into the attic, airflow from your vents is reduced and it might feel colder than it really is, even though the furnace is working fine.  

Do this: If you suspect you have leaky ducts, contact an HVAC technician who will inspect your ductwork and make a recommendation to seal or replace leaky ducts. 

Common problem #2: Furnace not turning on

A tripped breaker is the most common cause of a furnace that isn’t turning on. 

A furnace breaker may trip if the furnace is overworked.  

Do this: Before you reset your furnace breaker, you first need to double-check that your air filters are clean and your vents are open/unobstructed. Then, at the electrical panel, find the breaker marked HVAC or furnace and firmly press it off, then firmly press it on. 

If your breaker trips again, call an HVAC technician to diagnose the issue. A furnace breaker that keeps tripping is a signal of a larger issue with the electrical components. 

Other issues that will prevent your furnace from turning on:

  • The furnace is switched off. There is a power switch on your furnace that may be switched off. 
  • No power to the thermostat. If your thermostat is not receiving power, it cannot signal the furnace to turn on.
  • Improper thermostat setting. If the thermostat is set to cool or if the temperature is set too low on a thermostat, your furnace will not turn on.
  • Faulty Ignition switch. If your furnace is clicking but not running, the ignition switch is failing to light the pilot or burners. 
  • A triggered safety switch. Safety features signal your furnace to turn off when there’s a malfunction. 

If you’re struggling with a furnace that won’t turn on, contact an HVAC professional to help resolve the problem. 

Common problem #3: Furnace making grinding noises

A broken blower wheel is the most common cause of a grinding noise coming from your furnace. If you hear this sound, turn off your furnace immediately to prevent further damage. 

A loose blower wheel can cause fan blades to rub against the housing. 

Other causes for grinding noises include:

  • A loose bolt or other part which can get lodged inside the blower fan or motor
  • A broken blower mount which can cause the blower motor to lean or to fall
  • Worn bearings which may need to be inspected and lubricated 

Do this: If your furnace is making grinding or scraping noises, turn it off and call an HVAC technician to inspect and repair damaged parts. 

Do you need a professional for your furnace problems?

If you have a furnace problem that you can’t fix by flipping a switch, adjusting your thermostat, or changing a dirty air filter, we’re here to help.

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Cooper Heating & Cooling has been providing Colorado homeowners with eco-friendly, high-efficiency heating solutions for 40 years. When you contact us, you can expect fast 24/7 service from a Nate-certified HVAC professional, high-quality work done right the first time, and 100% satisfaction as proven by our A+ BBB rating. 

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