Broken heater

[Nuclear Fusion]

The heater on my Peugeot 308 seems to be broken, the fans only blow cold air. Are there any simple and cheap things I can do to fix this or is it a job for a garage?

 

[Nuclear Fusion]

Thanks for the responses, just checked the coolant and it's empty (oops). The engine temperature sensor does seem to work but it never gets too hot surprisingly, probably just because it's cold that it hasn't overheated yet

Needless to say, I will be buying some tomorrow and topping it up...