The gas grill regulator connected to your propane cylinder manages the pressure level of the fuel flowing from the cylinder to your grill burner. The valve mechanism and hoses connected to the regulator can wear out over time. The regulator may not function properly or the valve inside may lock down almost in the closed position so you get a very small or non-existent flame on the burner. You can buy replacement regulators at stores that sell gas grills, including hardware stores and specialty shops, or you can order one online from the manufacturer.
Apply spray lubricant to the connectors on the end of the old regulator hoses where each hooks up to the grill and to the gas cylinder. There will usually be a hose connection for each burner on your grill. For example, you'll have three connectors on a grill with two interior burners on the main cooking area and one side burner for cooking foods in a saucepan or skillet.
Unscrew the hoses from the grill and the gas cylinder with the pliers. Take the old regulator and hose assembly with you to the store for locating the correct replacement or use the model number and brand of your grill.
Twist on the large regulator connector to the valve on your gas tank and tighten with your hand only. Using pliers to tighten this end may crack the plastic connector shell.
Hook up the connectors on the other hoses to the valves on your gas grill. Rotate the connectors with your fingertips until they are hard to turn and then finish with half a twist on each connector with your pliers.
Mix liquid soap and water in a plastic pail until frothy. Submerge the sponge to soak up suds.
Open the tank valve on the gas cylinder. Check the control knobs on the grill to confirm they are in the closed and locked "Off" position.
Squeeze soap foam onto all connections on each end of the regulator to watch for fast-popping bubbles. This indicates a leak. If you see bubbling or smell gas, close the tank valve completely and start over with the connections.