Clogged Heater Core Symptoms

Many people don’t know the difference between a clogged heater core and an air filter. Clogged Heater Core Symptoms are one of the most common problems with furnaces, and there are many signs that you might need to call your HVAC technician to get it fixed.

Clogs can happen for many reasons like improper installation, dirt accumulation in the heat exchanger coil, or even a pet who likes to roll around in its litter box in front of your furnace. In this blog post, we will discuss 9 Clogged Heater Core Symptoms so you will be able to determine when it’s time for a repair.

Clogged Heater Core

How To Know When A Heater Core Is Plugged?

The first sign that you’re experiencing problems with your heater is when the heat doesn’t come from any registers. You can feel the air, but it’s chilly and not very warm-feeling at all! A plugged core may be causing this issue – so let’s do a quick test to find out which way it goes before spending too much time troubleshooting an expensive repair bill.

  1. Always check the coolant level in your radiator and overflow tank before starting the vehicle. Low fluid can be a major reason that there’s not enough circulating into it to warm up, so make sure you have equal parts antifreeze with water filling them again as needed.
  2. The smell of antifreeze, wetness on the passenger side floor, and a greasy mist inside your car’s windshield when you turn on its defroster mode may indicate that there is leaking in one of their heater cores. A replacement will be necessary to fix this problem before more damage occurs, or else they’ll keep losing fluid until it has been fixed.
  3. For best results, start by warming up the engine and leaving it in Park or Gear with the parking brake on. Next release hood latch to let air flow through system until temperature reaches operating levels
  4. To find out if your car’s temperature gauge is running correctly, locate the digital readout on an analog gauge and make sure it ranges from 190 degrees Fahrenheit to 220 degrees. If there are no numbers or markings indicating temperatures range in this area, then you may have problems with either coolant levels (which should be between 0-8)or thermostat settings, which will dictate how far up towards redline they go before shutting off again.
  5. In order to check the engine block for heat, touch it down near where you will find your thermostat. If there is no sign of warmth, then move on to other parts in need, like an upper radiator hose and its corresponding location on top of the car’s frame next.
  6. Locate the smaller hoses that go into your firewall on the right side (passenger) of the vehicle. In some cases, this may not be all that easy, and you will have to crawl underneath in order to find them, but if I am able, it takes about two seconds tops! If both these pipes are hot or warm, then there’s no doubt something is wrong with either one – most likely due to a clogged heater core unless otherwise specified by other symptoms listed below. If only one hose was warming up instead? Check for leaks near where they’re connected at the radiator end before moving forward).
  7. If the heater core hoses are not easily accessible and you have no desire to attempt unclogging them yourself, at least Wayne’s determined how they were able to get access in order for a qualified technician. If these aren’t too difficult an obstacle, then try flushing out your vehicle with garden water while shutting off all power sources- including lights! Let it sit long enough so that when done cleaning, there will be plenty of time before driving again or setting off on another trip.
  8. To install a drain bucket underneath your vehicle, use two different types of clamps: one with screwdriver heads and another type for channel locks. Make sure you identify which hose connects where so when reinstallation time comes around again-it will be easier! Once everything is properly drained, remove both screws or hinges from their respective locations before removing them completely from beneath the car’s hoodie (depending on what kind they were).
  9. Ever wonder how to get rid of winter’s settled on your car? One way is by using a garden hose and inserting it into the inlet tube. Be careful with which pressure you turn on because some hoses can handle up 100 lbs per square inch–which could burst open any seams near where water meets the air conditioner unit! Turn that stream until all excess grime has been blown away from inside the vehicle, making this task much more manageable than trying other methods such as wiping down or vacuuming out dirt particles first before switching over, so nothing gets missed.

In order to fix a broken heat system, you need to replace the hoses and tighten clamps if they are loose. It’s also important that antifreeze be added in case burping is needed after adding fluid or when putting caps back on at startup with an open radiator cap!

Check under your vehicle for leaks before topping off as necessary until the thermostat gauge gets close enough towards operating temperature – You should now feel plenty of hot air coming from registers throughout the engine bay again. The goal here isn’t just making things work but rather doing everything possible, so no one has their car broken down by negligence because we’re pros now 😉

What Are Clogged Heater Core Symptoms?

Clogged Heat Exchanger Coil

If dirt settles in the coils of your heater, it can cause a lot of problems like reduced efficiency, which means that you are spending more money on energy bills than usual.

Clanking Sounds

Loud clanking noises coming from inside the unit indicate something wrong with its components, possibly resulting in high utility bills or even complete failure!

Clogged Evaporator Coil 

When air from your furnace is not cooled properly, it means that something is wrong with its components which will result in reduced heating efficiency.

Cluttered Cabinet Space

If you notice that there are parts lying around on top or even inside of your unit, then this could be an indication of problems with your system’s internals. This symptom may also come up if the previous owners were DIY enthusiasts who wanted to “repair” their own heaters but didn’t know what they were doing!

Decreased Indoor Temperature

It might seem counterintuitive, but some furnaces don’t work as well at lower temperatures than higher ones because they need to maintain a certain temperature inside your home.

Clogged Filter

You will need to check the filter every few months and change it when necessary. If this symptom is present, your furnace won’t be able to circulate air properly or warm up.

Decreased Airflow Speed

an old furnace may have decreased airflow because normal wear and tear made some parts ineffective at their job

Noisy Operation

Lack of insulation between the heater and the outdoor environment can cause a lot of noise.


If your heater is not working and you suspect a clogged core, it’s important to get an expert opinion as soon as possible. A blocked heating system could prevent warm air from circulating throughout the house and causing damage that can be costly or impossible to fix. That’s all we have on Clogged Heater Core Symptoms.

Frequently Asked Questions

How do you unclog a heater core?

It can be done by pouring a large pot of boiling water down it. The heater core is actually not clogged in most cases but rather iced over. If there is any uncertainty, the best course of action is to turn off power to the unit or disconnect electricity leading up to it which will cause the ice blockage to melt.
Doing this in an indoor area that is well-ventilated with plenty of exterior entry points for when hot steam rises out through windows helps avoid lung issues, burns, carbon monoxide poisoning, and the risk of electrocution.

Will a radiator flush unclog the heater core?

A common symptom of a clogged heater core is an engine heater not working correctly. A radiator flush can also be used as a solvent to loosen up any grime buildup in the engine caused by neglecting required maintenance or infrequent fluid flushes. In general, before using a flush, check your vehicle’s owner’s manual for its recommended procedure and follow it carefully.

Can you drive with a clogged heater core?

You should bring your car into the shop for this. It’s not worth risking an accident while trying to plow through snow. Yes, the air coming out will be cooler, but you want it to also be plenty warm enough so that you can defrost your windshield easily at stoplights or gas stations.
If you have a clogged heater core, it would definitely impact how well your heating system operates – and while there are some “hacks” for this problem, they may void any factory warranty on the heating system in your vehicle.

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