7 Reasons Your Car Heater Isn't Working Properly

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As summer dissipates through fall and stretches into winter, most drivers aren’t too worried about their car’s heater. It worked last year, and the year before that, why wouldn’t it work this year? Well, fine drivers(G&Gers, Guiders, Garage Gnomes? We’ll pick a name later.), life tends to throw curveballs at you, and guess what, your heater isn’t working properly anymore.

Heaters aren’t the mysterious beast most make them out to be. Heating systems consist of a heater core, a heater fan, the car’s coolant system, and your HVAC controls. As hot coolant is drawn into the heater core, the heater fan, controlled by the HVAC controls, blows that heat into the cabin as the cooled coolant returns back to the system. Though a simple system, a number of issues can arise causing your heating system to not function properly. 

And now is the perfect time to learn what can go wrong and decipher your car’s heater is kaput. Follow along as The Drive’s whip-smart info team breaks down the top reasons why your car heater isn’t working properly and how to fix them. Let’s heat this mother up!

A host of thermostats.

7 Reasons Why Your Car Heater Isn’t Working Properly? 

As with any faulty object, any of a host of reasons can prove to be the leading culprit. To better diagnose your car’s on-the-fritz heating system, let’s get into the reasons it can go bad.

Faulty Thermostat

A faulty or broken thermostat is the most common cause of your car’s failing heat. Stuck open or stuck closed, the part can not only cause issues with your heat but also your engine’s cooling system. One becomes an issue of comfort, the other becomes an issue of “Oh no, I’ve borked my engine.”

Low Antifreeze/Coolant

The second-most common issue is low antifreeze or coolant. When your coolant/antifreeze levels drop, the hot fluid can’t make it to the heater core, and thus, your cabin remains chilly. This can occur if the engine is working too hard and overheats or if it wasn’t properly filled.

A close up of your HVAC controls. 

Faulty Heater Fan

While you may be getting hot coolant/antifreeze into the heater core, the heater fan, the part that actually blows the heat into the cabin, can break or suffer an electrical short.

Faulty Blower Motor Resistor

If the blower motor resistor is broken, you might have issues setting the fan speed or getting air at all.

Clogged Heater Core

Occurring less often than the above issues, debris and particulates that make it into the coolant system can clog your heater core. This can happen when a radiator rusts from the inside or if debris gets through the radiator and lodges itself into the heater core. Either way, you’re looking at refurbishing your heater core or straight-up replacing it.

Leaky Radiator

A leaky radiator could prevent coolant from reaching your heater core and could damage your engine, at worst.

Faulty HVAC Controls

Simply put, your car’s buttons, knobs, or haptic feedback touchscreens may not be triggering the heating system. Shorts, broken dials, and bad touchscreens can all lead to malfunctions that prevent your heater from working. 

Faulty Wiring or Blown Fuses

Similar to your broken HVAC controls, your car’s wiring could be broken or have a short in it. This would mean the heater isn’t triggered when the driver commands it to function. Not good. 

Heater vents. 

Here’s How To Fix a Broken Thermostat

To assuage your fix-it fears and show you just how easy DIY repairs can be, The Drive put together an easy-to-follow guide on how to fix a broken thermostat. You will need to purchase new coolant and a new thermostat.

Safety

Working on your car can be dangerous and messy, so here’s exactly what you’ll need to ensure you don’t die, get maimed, or lose a finger and that you keep your jeans, shirt, and skin spotless—hopefully.

  • Mechanic’s gloves
  • Safety glasses

Everything You’ll Need To Fix a Broken Thermostat

We’re not psychic, nor are we snooping through your toolbox or garage, so here’s exactly what you’ll need to get the job done. 

Tool List 

  • Drain bucket
  • Selection of wrenches

Parts List

  • Coolant
  • New thermostat

Organizing your tools and gear so everything is easily reachable will save precious minutes waiting for your handy-dandy child or four-legged helper to bring you the sandpaper or blowtorch. (You won’t need a blowtorch for this job. Please don’t have your kid hand you a blowtorch—Ed.)

You’ll also need a flat workspace, such as a garage floor, driveway, or street parking. Check your local laws to make sure you’re not violating any codes when using the street because we aren’t getting your ride out of the clink.

How To Fix a Broken Thermostat

You’re done!

A man filling antifreeze.

How To Fix Low Antifreeze

The second-most common culprit is that your car has low antifreeze or coolant. Thankfully, it’s far less time-consuming than replacing your thermostat. All you’ll need is a funnel and new coolant. Ready?

That’s it!

Get Help With Your Car’s Heater From a Mechanic On JustAnswer

The Drive recognizes that while our How-To guides are detailed and easily followed, a rusty bolt, an engine component not in the correct position, or oil leaking everywhere can derail a project. That’s why we’ve partnered with JustAnswer, which connects you to certified mechanics around the globe, to get you through even the toughest jobs. 

So if you have a question or are stuck, click here and talk to a mechanic near you. 

FAQs About Car Heaters

You’ve got questions, The Drive has answers!

Q: How Can I Heat My Car Without a Heater?

A: To borrow a phrase from the most excellent Archer, “Noooooooope!” We’re gonna need you to absolutely stop thinking about how you can heat your car without a heater. Why? Because you can’t. Any form of outside heat like a space heater, whether electric or propane, is a surefire way of setting yourself and your car on fire. And if you try to emulate some sketchy blog’s “Life Hack,” you’ll end up like this lad. And you don’t want to be this lad. He’s a bad role model. 

Q: Is There a Fuse For The Heater In My Car? 

A: Your car’s heater does indeed have a fuse. You can check to see if the heater fuse is shot by looking inside your fuse box. You’ll need your car’s dusty manual to find out where your fuse box is and which fuse is for the heater.

Q: How Much Does a New Thermostat Cost?

A: The average cost of a thermostat is about $45, but if you’re replacing the thermostat, you’ll also need to factor in new coolant, which will set you back around $8-$15 a gallon.

Q: How Often Do You Need To Flush Your Coolant?

A: The common thinking is every five years or 100,000 miles. Yet, that could change if you’re having issues with your heat or your car overheating. 

Q: Why Is My Car Blowing Cold Air When the Heat Is On?

A: Your heater is broke!

Q: How Much Is a New Heater Core?

A: Heater cores generally run between $100-$300. The real cost is due to labor, as heater cores aren’t something most DIYers normally tear into due to their deep locations within the engine bay or underneath the dashboard.

Q: How Much Does It Cost To Fix a Heater Core?

A: If you’re doing it yourself, you’ll pay just the cost of the new parts. If you have a professional fix it, you’re looking at an $800-$1,000 bill.

Q: How Long Does a Heater Core Last?

A: Most heater cores are designed to have very long use-lifes, averaging about 10-15 years. Obviously, if you put strain on your heater core or fail to remedy a fault when it occurs, such as the heat not working as well as it once did, that life will be considerably shortened.

Featured Heater Products

Evans High-Performance Waterless Engine Coolant

Zerex Original Green Antifreeze

Star Brite Star-Cool Premium Synthetic Engine Coolant

Got a question? Got a pro tip? Send us a note: guidesandgear@thedrive.com

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