Cracked Heat Exchanger Symptoms: All You Need to Know

How do you know if your heat exchanger is broken? It is not always evident that the heat exchanger is cracked, since the furnace could keep running for a while regardless. However, a cracked exchanger is dangerous for the household inhabitants. 

It is essential to figure out a problem with the heat exchanger as soon as possible. This article describes how you can figure out something is wrong with the heat exchanger, but if you need additional assistance, check this article.

What are the symptoms of a bad heat exchanger? 

It is difficult to figure out that there is something wrong with the heat exchanger because even with a crack, the furnace will continue working. In addition, if there are carbon monoxide leaks, it is impossible to know it since it is odorless unless a detector is installed in the house. 

You can expect some indirect signs that could signify that your heat exchanger requires a reparation. Here are some of the symptoms:

  • External cracks
  • Soot build-up
  • Weird smell
  • Visible corrosion
  • Water leaks
  • Health problems 

1. Soot build-up

When the heat exchanger is cracked, the furnace will produce a lot of soot or carbon buildup. This happens when the furnace is not burning all the gas (incomplete combustion). 

Incomplete combustion is a sign of faulty burners, but it is also a sign of a cracked heat exchanger. It is possible to detect soot during system maintenance or if a technician is looking purposely for it to evaluate the presence of cracks. 

The system has to be disassembled to get to the gas chamber, where it is possible to see the presence of soot. Again, a professional technician should do this operation since it can be dangerous for someone with no experience or technical skills. 

2. Visible cracks

With the normal wear and tear, the heat exchanger can crack. After many years, an old system is subject to internal damages due to the stress and corrosion of its parts. In addition, the heat exchanger is made of metal, and it has to endure extreme temperatures. 

The constant changes between hot and cold make the metal expand and contract. Finally, those swings make the furnace and the heat exchanger cracks after many years. 

It is expected that the material gives way with time, and cracks form. Therefore, when the furnace is over ten years old, it is wise to perform regular inspections to verify that there are no cracks. 

The only way to verify the presence of a crack is to inspect the internal structure of the furnace. If the furnace is broken, then the heat exchanger is cracked too. 

3. Unusual smell coming from the furnace

Another sign of a cracked heat exchanger is the presence of an unpleasant smell or a formaldehyde-like odor. The fumes coming out of the cracks are toxic and should not be inhaled. 

In addition, when the fumes are inhaled, health symptoms can show up, such as headaches or even a flue. 

If you smell such an odor, it is time to call a technician to do a full inspection, but do not forget to shut off the system to prevent the production of more fumes or gas leaks. 

4. Health problems 

Cracks in the heat exchanger cause leaks of gas inside the house. The gases that could leak are sulfur dioxide, nitrous oxide, and carbon monoxide. Those gasses have adverse effects on people. The symptoms that people can experience are:

  • Nausea
  • Eyes irritation
  • Insomnia
  • Headaches
  • Flue
  • Dizziness
  • Shortness of breath

The side effects appear when the house inhabitants are near the furnace and can inhale the fumes and gasses. The solution is to call the repair service immediately and shut off the furnace immediately. 

5. Water leaks

In some cases, when there is water leaking from the furnace, one of the causes is a malfunctioning heat exchanger. For example, water might leak if there are cracks in the heat exchanger. 

If that happens, you should not try to resolve the issue yourself; instead, have a qualified technician resolve the situation. 

6. Corrosion

Corrosion usually occurs with time and usage. Signs of deterioration on the furnace can signify that the heat exchanger is cracked or is about to crack. But, it is never a good sign to see corrosion building up on a furnace.

Corrosion occurs because of a chemical reaction between the furnace’s materials, which are made of metals, and water or other elements. 

7. Yellow furnace flame

In general, the ignition flame is blue. So the heat exchanger performs appropriately if you see a stable blue flame. But if you see it becomes yellow, it signifies a problem with the heat exchanger or the burners. 

An unsteady or flickering flame is another sign of an issue or malfunctioning heat exchanger. 

What you should do in case of a heat exchange crack?

The first strategy is to prevent cracks in the heat exchanger. A furnace could continue running for a long time without anyone noticing. Often the only way to prevent or discover a crack in the heat exchanger is to have yearly maintenance done. 

During the inspection, all the signs that indicate the presence of a crack will show up, and a qualified technician can advise what to do. 

However, if it doesn’t come up during the yearly maintenance, and you suspect that the heat exchanger is broken, the first thing to do is get professional help. The technician can tell you that there is nothing wrong or locate the crack and tell you to replace the heat exchanger. 


A heat exchanger that has a crack can be dangerous for the household. Often it is necessary to have a full inspection done to locate the crack or determine if the heat exchanger needs to be replaced. In the worst case, if the damage is too extensive, you might need to replace the entire furnace. 

If you are unsure about the presence of cracks in the heat exchanger, it is better to have it serviced by a professional technician.