When repairing a space heater, clean it first, as dirt on some parts of the heater may cause it to stop working. Unscrew the base of the heater to find its cabin space, and clean the dirt out of it. If the space heater is fueled by gas, check to see if the nozzles are dirty, and clean them. Clean out the heating elements and ceramic plates, as heaters don't work as well if those parts are dirty.
If that didn't work, check to see if all of the power cords remain undamaged and connected to the heater. Check the wires that are connected to the electrical heating elements inside of the heater. If the appliance heats up and doesn't spread the heat, make sure the power cords that power the motor that turns the heater fan are undamaged as well. If any of the wires are broken, repair them yourself, or hire a professional to do so. Attach the disconnected wires.
Check to see if the thermostat on the heater is working, and replace it if needed. The thermostat might be broken if the heater doesn't respond to controls or if it turns off too quickly. Check to see if the heating element is damaged; some examples of damages include cracks and color changes. Hire a professional to repair the heater if you find any signs of damage.