why is car heater not working

[SanAsher]

The most common reason a car heater isn't working is a low coolant level or a problem with the thermostat. The heater core, which is a small radiator under your dashboard, relies on hot engine coolant flowing through it to produce heat. If there's not enough coolant, or if the coolant isn't getting hot because the engine thermostat is stuck open, you'll get cold air.

Before assuming the worst, check your coolant level in the overflow reservoir when the engine is cool. If it's low, topping it off might solve the problem immediately, but you should also investigate for leaks. Another quick check is to feel the upper and lower radiator hoses after the engine has run for a few minutes; if they aren't getting warm, the thermostat is likely stuck open.

For more complex issues, here are the primary culprits and their typical symptoms:

Problem Cause	Typical Symptoms	Approximate Repair Cost (Parts & Labor)	Frequency of Occurrence
Low Coolant Level	No heat, possible temperature gauge reading high	$20-$50 (for coolant top-up)	Very Common
Faulty Thermostat	Engine takes a long time to warm up, no heat	$150-$400	Common
Airlock in Cooling System	No heat, inconsistent temperature gauge	$100-$200 (system bleed)	Common
Clogged Heater Core	No heat, foggy windows, sweet smell inside car	$500-$1,000	Less Common
Blender Door Actuator Failure	Airflow comes from wrong vents, clicking noise from dash	$300-$600	Common
Heater Control Valve Failure	No heat, but engine warms up normally	$200-$450	Less Common

A clogged heater core is one of the more expensive and involved repairs. The core's small tubes can become blocked by debris or old coolant, preventing circulation. A failing blender door actuator, which is a small motor that directs airflow, won't stop heat from being generated but will prevent it from reaching the cabin, often accompanied by a repetitive clicking sound from behind the dashboard. If you're not comfortable checking coolant levels or diagnosing these issues, it's best to take the car to a professional mechanic to avoid engine damage.

[VonElliot]

First thing I'd check is the coolant. Pop the hood when the engine is cold and look at the plastic overflow tank. There are "MIN" and "MAX" lines on the side. If it's below the minimum, that's probably your issue. Topping it off might get you heat again. But if it keeps getting low, you've got a leak somewhere that needs fixing.

[BrookeDella]

As a guy who likes to fix things myself, I start with the simple stuff. Is your engine actually getting up to full temperature? If the temp gauge stays low, the thermostat is stuck open. Next, feel the two hoses going through the firewall into the heater core. If one is hot and the other is cold, the core is likely clogged. Also, listen for a clicking sound from your dashboard when you change the temperature setting—that’s a classic sign of a broken actuator motor.