Hi , i was making a brazier , as a tutorial on unreal engine 4 , it added a particle of fire , but i am getting gray squares instead of fire , sorry for the silly question i started to learn this 2 days ago 
, Thanks a lot for your help :).
Ye, I am getting this visual bug aswell, it seems to only be on the tutorial brazier fire.
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I have the exact same problem.
Same problem here too:
https://forums.unrealengine/showthread.php?60906-Unreal-Tutorial-Particle-System-doesn-t-seem-to-have-any-actual-fire
Will close this thread. For further help take a look at the upper posted thread 
Edit:
Will just add the solution into this thread 
-open the particle system
-switch to the content browser and select the “M_smoke_subUV_blackbody” material
-go back into the particle system - click onto “required” - add the material
-now it should work