* Thermostat: The thermostat regulates the flow of coolant to the engine. If it's stuck open, the engine won't get hot enough.
* Coolant level: If the coolant level is low, there won't be enough fluid to circulate and transfer heat from the engine to the heater core.
* Water pump: The water pump circulates the coolant through the engine and heater core. If it's not working properly, the coolant won't flow and the heater won't get hot.
* Heater core: The heater core is a small radiator located in the dashboard. It transfers heat from the coolant to the air that flows into the passenger cabin. If the heater core is clogged or damaged, it won't be able to transfer heat efficiently and the cabin will stay cold.
If you're not comfortable checking these things yourself, you can take your car to a mechanic for diagnosis and repair.
