If your car's heater isn't working, one possible reason is a clogged heater core. A clogged heater core can be caused by a build-up of sediment or rust, and it can prevent heat from being transferred from the engine to the cabin of the car. If you think your heater core might be clogged, there are a few things you can do to try and unclog it.
One option is to flush out the heater core with water. This will help to remove any sediment or rust that might be causing the blockage. To do this, you'll need to disconnect the hoses that lead to the heater core and then run water through them until it comes out clean. Once you've done this, reconnect the hoses and turn on your car's engine to see if the heat is now coming through.
Another option is to use a chemical cleaner specifically designed for unclogging heater cores. These cleaners contain acids that can dissolve sediment and rust, clearing the way for heat to flow freely again. Be sure to follow the instructions on the cleaner carefully, as using too much of it can damage your car's engine.
If neither of these methods works, then you may need to have your car's heater core replaced. This is a more involved repair than simply unclogging a blocked hose or flushing out sediment, so it's best left to a professional mechanic