Heat Not Working In Car When Idle

Heat Not Working in Car When Idle: Causes and Solutions

When the temperature drops, a functioning car heater is essential for maintaining a comfortable and safe driving environment. However, if your car’s heat is not working when idling, it can be a frustrating and potentially dangerous issue. This article will explore the various causes of this problem and provide step-by-step solutions to get your car’s heat up and running again.

Understanding the Problem

When your car’s heat is not working when idling, it means that the heater core is not receiving hot coolant from the engine. This can be caused by several factors, including:

  • Low coolant levels: If the coolant level is low, there may not be enough fluid to circulate through the heater core and provide heat.
  • Air in the cooling system: Air pockets in the cooling system can prevent coolant from flowing properly to the heater core.
  • Faulty thermostat: A malfunctioning thermostat can prevent the engine from reaching its optimal operating temperature, which can result in insufficient heat production.
  • Clogged heater core: Debris or sediment can accumulate in the heater core, restricting coolant flow and reducing heat output.
  • Electrical problems: Faulty wiring or switches can disrupt the electrical signals that control the heater fan or other components of the heating system.

Troubleshooting and Solutions

To troubleshoot and fix the problem of heat not working in car when idle, follow these steps:

  1. Check coolant levels: Open the coolant reservoir and check the fluid level. If it is low, add coolant as needed.
  2. Bleed the cooling system: If there is air in the cooling system, bleed it by following the manufacturer’s instructions. This involves opening a bleeder valve on the engine or radiator to release any trapped air.
  3. Inspect the thermostat: Locate the thermostat and check if it is opening and closing properly. If it is stuck closed, replace it with a new one.
  4. Flush the heater core: If the heater core is clogged, flush it by using a garden hose to backflush the core. This will remove any debris or sediment that may be restricting coolant flow.
  5. Check electrical connections: Inspect the wiring and switches related to the heating system. Look for any loose connections or damaged wires. Repair or replace any faulty components as needed.

Types of Car Heaters

There are two main types of car heaters:

  • Engine coolant heaters: These heaters use the engine’s coolant to generate heat. The coolant is circulated through a heater core, which transfers the heat to the air inside the car.
  • Electric heaters: These heaters use electricity to generate heat. They are typically used in smaller vehicles or as supplemental heat sources in larger vehicles.

Advantages and Disadvantages of Car Heaters

Type of Heater Advantages Disadvantages
Engine coolant heaters More efficient Can be slower to warm up
Electric heaters Faster to warm up Less efficient

How to Use a Car Heater

To use a car heater, follow these steps:

  1. Start the engine: Turn on the engine to start the coolant circulation.
  2. Set the temperature: Adjust the temperature knob or dial to the desired temperature.
  3. Turn on the fan: Turn on the fan to circulate the heated air throughout the car.
  4. Direct the airflow: Use the vents to direct the airflow to the desired areas of the car.

What to Do If Your Car’s Heat Still Doesn’t Work

If you have followed the troubleshooting steps and your car’s heat still doesn’t work, it is recommended to seek professional assistance from a mechanic. They can diagnose the problem more accurately and perform any necessary repairs or replacements.


Heat not working in car when idle can be a frustrating issue, but it is often caused by simple problems that can be easily resolved. By following the troubleshooting steps outlined in this article, you can diagnose and fix the problem yourself in most cases. However, if the issue persists, it is advisable to consult a qualified mechanic for further assistance.


Q: Why is my car heater blowing cold air when idling?
A: This could be due to low coolant levels, air in the cooling system, a faulty thermostat, a clogged heater core, or electrical problems.

Q: How can I tell if my car’s thermostat is bad?
A: Signs of a bad thermostat include overheating, underheating, or fluctuating engine temperatures.

Q: Can I flush my car’s heater core myself?
A: Yes, you can flush the heater core yourself using a garden hose and following the manufacturer’s instructions.

Q: How much does it cost to fix a car heater?
A: The cost of repairing a car heater depends on the cause of the problem and the extent of the repairs required. It can range from a few dollars for a simple fix to hundreds of dollars for more complex repairs.

Closing Statement

Maintaining a functioning car heater is crucial for a comfortable and safe driving experience, especially during cold weather. By understanding the causes and solutions of heat not working in car when idle, you can diagnose and fix the problem yourself in many cases. However, if the issue persists or you are not comfortable performing the repairs yourself, do not hesitate to seek professional assistance from a qualified mechanic.


The information provided in this article is for general guidance purposes only and should not be taken as professional advice. It is recommended to consult a qualified mechanic for any specific car repair or maintenance issues.