Fill 'Er Up
Before you panic, make sure your Shark Steam Mop's reservoir is filled with clean water -- no water means no steam. Once you've filled the tank to the fill line, give your mop about 30 seconds to heat up and produce steam before moving on to other troubleshooting procedures.
Steam Mode Engaged
Simple mechanical tweaks might solve your steamy (or steam-less) woes. As you fill the water tank, keep an eye out for the water intake tube. If the tube is bent, straighten it out to ensure that it reaches the bottom of the tank.
If your Shark has a steam-locking collar, as featured on the Steam and Spray models, turn it to the "Steam and Spray" position rather than the "Spray Only" position.
Cut Through Calcium
Over time and use, calcium and mineral deposits may build up in your Shark mop's nozzle, inhibiting the release of steam. When this happens, Shark recommends cleaning the nozzle to remedy the issue.
To get the steam flowing again, grab the nozzle cleaner included with your mop. If you don't have one, a straightened-out paper clip works just fine, too.
Unplug the Shark and remove its head. You'll spot a small hole -- this is the nozzle from which the mop releases steam. Simply insert the end of your cleaner or paper clip into the hole and gently move it up and down a few times to clear away steam-stopping buildup.