Here's what you need to know:

* Function: Bleed valves are small valves that allow you to release trapped air from your radiator system. Air bubbles can prevent proper heating and circulation of water.

* Location: The star symbol is usually found on the top of the radiator, close to the bleed valve itself.

* Purpose: When you see a star on your radiator, it means there is a bleed valve there. You can use a small bleed key or screwdriver to open the valve and release trapped air.

* Bleeding: If your radiator is cold at the top while the rest is hot, it's a sign that you need to bleed the air out.

Important note: It's always a good idea to consult your radiator's manual or contact a professional plumber if you're unsure about how to properly bleed your radiator system.