How to tell if a furnace is bad?

Author: Nat Wisozk DVM  |  Last update: Thursday, June 5, 2025

Warning Signs That You May Need A Furnace Replacement
  1. 1 – Frequent Repairs. It's not abnormal to need furnace repairs once a season. ...
  2. 2 – Cold Air. ...
  3. 3 – Strange Noises and Odors. ...
  4. 4 – Yellow Pilot Light. ...
  5. 5- Increased Dust. ...
  6. 6 – Increased Heating Bills. ...
  7. 7 – Poor Temperature Control.

How do I know when my furnace needs replacing?

Five signs you need to replace your boiler or furnace
  1. Uncomfortable or uneven temperatures. An aging heating system will struggle to heat your home evenly and consistently, especially on colder days. ...
  2. Unusual sounds. ...
  3. A yellow flame. ...
  4. Rust or other corrosion. ...
  5. Over 15 years old.

How do you know if your furnace is bad?

Here are ten red flags you need to look out for to tell if your furnace is dying:
  • Frequent Service Calls. Constantly having to repair your furnace may be the first sign that it's failing. ...
  • Flu-Like Symptoms. ...
  • Strange Noises. ...
  • An Old Furnace. ...
  • Dry Air. ...
  • Flame Color. ...
  • Poor Temperature Control. ...
  • Higher Utility Bills.

How can I test my furnace?

Check the thermostat settings.

The furnace will not come on unless the ambient temperature drops below the setpoint. To test the furnace, temporarily set the thermostat five to ten degrees higher than you normally would to see if it comes on, then return the thermostat to its normal setting when the test is complete.

How can you tell when your furnace is going out?

Pilot flame color changes

A gas furnace should have a vibrant or bright blue flame. When you see a weak and wavy or flickering flame, this indicates gas is not being completely burned. Pilot light color changes are another indicator that carbon monoxide is not venting away from the system safely.

Warning Signs your furnace needs repaired or replaced

How much does a new furnace cost?

You should expect to spend between $3,800 and $12,00 on a new furnace, including both the unit and installation costs. Factors influencing the price include the type of furnace (gas, electric, or oil), the unit's efficiency rating, and the complexity of the installation.

How do I know if my thermostat or furnace is broken?

A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.

How much does it cost to have your furnace checked out?

A furnace inspection costs an average of $80 to $100. Your cost may increase if more furnace repairs are needed, or based on the specifics of your HVAC system. If detrimental issues are uncovered, you'll be quoted for the repair or potential replacement of your HVAC equipment.

Who do I call if my furnace isn't working?

If your furnace's problems continue, contact an HVAC expert. Also, if you notice discoloration when you check the pilot light, get professional help. If there are cold spots in your home, even though hot air is coming out of the air vents, the issue could be different from your furnace not working.

How to inspect a furnace?

Burners & Manifold
  1. Look at the burner assembly and manifold. In-shot burners are common.
  2. Look at the cover panel. Look for indications of water, corrosion, and blockage.
  3. Look at the air shutters (if present).
  4. Check the burner ignition sequence during operation (using the thermostat, a normal operating control).

What fails first on a furnace?

If the flame sensor fails, your furnace may not be able to start or may shut down shortly after starting. Common causes of flame sensor failure include corrosion, dirt buildup, or a broken wire. The gas valve controls the flow of gas to the furnace. If the gas valve fails, your furnace won't be able to produce heat.

What is the life expectancy of a furnace?

The Average Furnace Lifespan

A well-maintained furnace can last at least 15 to 20 years, but completing annual maintenance and being diligent with repairs can extend its life even longer.

What is the most common furnace failure?

One of the most common furnace problems is a malfunctioning thermostat. A sure sign your thermostat isn't working properly is if your fan is constantly running. This will cause your thermostat battery to run, and cause your furnace to work inefficiently.

When should I worry about my furnace?

You should be concerned if your furnace makes strange noises, blows cold air, cycles on and off frequently, or significantly increases your heating bills. Also, if it's over 15 years old and requires frequent repairs, it may be time to replace it.

Is replacing a furnace easy?

Replacing a furnace is a labour-intensive undertaking and is pretty difficult. There are a large variety of factors that need to be considered and accounted for. It is never recommended to replace a furnace yourself as the appliance is a major investment and should be handled by professionals.

How do I know if I need a new furnace blower?

10 Signs That Your Furnace Needs a New Blower Motor
  1. No Airflow From Your Vents. ...
  2. Higher Energy Bills. ...
  3. Strange Noises When Your Furnace Ignites. ...
  4. Strange Smells. ...
  5. The Blower Stops Working After You Turn On Your Furnace. ...
  6. Constant Thermostat Adjustments. ...
  7. There Is Cold Air Coming From Your Furnace. ...
  8. Your Furnace Doesn't Ignite.

How do you diagnose a furnace problem?

How to Troubleshoot a Furnace: 7 Steps to Finding a Solution
  1. Inspect the Thermostat. ...
  2. Change the Furnace Filter. ...
  3. Confirm the Furnace Is Getting Power. ...
  4. Make Sure the Circuit Breaker Isn't Tripped. ...
  5. Check the Vents for Blockage. ...
  6. Make Sure the Front Panel Door Is Secure. ...
  7. Call a Professional.

How can I get a new furnace for free?

Apply for a grant

The Federal Low Income Home Energy Assistance Program (LIHEAP) helps low-income Americans with heating and cooling expenses. Apart from small grants, LIHEAP offices also help consumers find resources to help pay for the cost of replacing furnaces and air conditioners.

Can I fix my furnace myself?

Can I Fix My Furnace Myself? Yes, simple tasks like changing the air filter or resetting the circuit breaker are safe DIY options. For complex issues, consult a licensed HVAC professional.

Does insurance cover furnace failure?

While there's no such thing as furnace or boiler replacement insurance, homeowners insurance may cover the cost to replace your furnace or boiler if it's damaged or destroyed by a covered peril.

How do you know your furnace is going out?

If you put your hand to your home's heating registers and feel cold air blowing out instead of warm air, this is one of the signs your furnace is going out. Oftentimes, cold air coming from vents means that your furnace's blower fan isn't functioning correctly.

How often do furnaces need to be serviced?

Ideally, you would have your furnace serviced at least once a year. To elaborate on that point, you should have your furnace serviced at least once a year to catch any problems early on and to keep your furnace in top condition. Professional maintenance and cleaning provide many benefits, which we'll cover next.

Why is my furnace not kicking in?

There are several reasons why your furnace may not turn on. The most common include a broken thermostat, gas line issues, clogged air filters, blocked ductwork, a tripped circuit breaker, and issues with the furnace itself.

How can people tell if their furnaces are broken?

One of the most obvious signs that a furnace needs repairs is that the unit is not doing its job. If your furnace is producing no heat or only a low level of heat regardless of your thermostat settings, schedule repairs.

Is it my thermostat or furnace?

Pay attention to how often your heating system cycles on and off. Frequent cycling could be a sign of thermostat problems as it struggles to maintain the desired temperature. If the system stays on for extended periods without adequately warming the house then the furnace might be working inefficiently.

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