HaI have a Q100 grill.
No that is not normal and the issue is regulator related. Before you head out to buy parts, try solving the problem this way. Turn the LP Tank Valve OFF. Disconnect the hose from the tank and wait 5 minutes. Them reconnect the hose to the tank and turn the Tank Valve ON Very, Very Slowly (Slow motion, slow). Once the tank valve is fully open, light the burner and turn it to high. Has the flame height returned to normal? Is so, you solved the problem. If it hasn't you will need to replace the grill hose/regulator assembly. You can purchase one at any home center or hardware store that sells gas grills and accessories. Be sure to take your old one with you for comparison purposes.
Hope this helped you to solve the problem. Happy Grilling!!
Weber Q Grill
on Sep 06, 2014