There are a number of factors that can contribute to your grill not getting hot. It’s recommended that you hire a licensed plumber to set up all gas lines and connections. The length of the gas line, the water column pressure and pipe diameter vary depending on the set up you choose. Assuming all lines and connections are configured to provide adequate pressure, here are other factors which may cause your grill not to get hot enough:
Check to make sure the burner is on the high setting. The low setting is when the knob is all the way to the left. Moving the dial to the right increases the flame height.
Regulator clogs or running gas through multiple regulators could decrease the pressure not allowing your grill to heat to the proper temperature.
NG vs LP Gas Setup
Running natural gas into a liquid propane set up. The orifice size of an LP set is smaller than an NG and may not be allowing enough gas through.