I have had my printer for 1 month, but have noticed now that the printer will start printing 3CM from the bed. I can see it doing the leveling and the nozzle will touch the bed, but when starting it will print in mid air. Not sure what is wrong. Sometimes the printer will print fine, other times it will be 3CM too high.
Please help.
Check that all the connectors to the limit switches are secure.
Hello @testtes71406496 …! 
Welcome to the Creality Forum…! 
This is not always a mechanical issue.
Check your slicer settings carefully to see what changed.
Use an stl file and test your printer again.
A 3mf file could contain information and a profile for a different printer
I worked out what the issue was, the power cord for the hot end is getting caught on the filament role when the filament is new. If I print the same STL 3 times, 1 out of the 3 will start to print 3cm from the bed. I actually think this is a bad spool location design, with all the other power cords in the way.
Glad to hear you figured out the problem. 
It’s not the best location for the filament roll. I’ve moved mine to the top but still working on the filament detector setup.
I still have to babysit it and make sure the cords have enough slack to move around and not get hung up on anything…
If your spool goes directly out to the right, you might want to print one that mounts to the same bolts but comes to the front of the printer