Gas Grill: Some burners won't light
When one or more burners won't light, a clog is often the cause. Remove the grates and the flavor bars and then check the burners for a clog such as a spider web inside the burner tubes. Check the ports on the sides of the burner tube for clogs as well, or for damage. If the grill has an igniter for each burner, look for a failed burner igniter. A failed grill manifold could also be the cause.
These repairs may help solve your Gas Grill problem:
Clean, repair or replace the gas grill burner
Regularly check and clean the burner tubes of spider webs and debris. Clean the burner tubes with a bottle brush or stiff wire, such as a straightened coat hanger. Check the gas ports (holes) for spills that could glog them. Clean the burner if necessary. Look for rust or damage on the burner bodies and replace a burner if it's damaged or rusted.
Clean, align or replace the gas grill igniter electrode
If the igniter electrode—also called the spark electrode—isn't sparking properly, first check the alignment and adjust it if it's misaligned. Clean the electrode if needed. If it's damaged, replace the igniter electrode. If it still won't spark, the battery could be weak, if your ignition system uses a battery. Replace the battery if necessary. If the igniter still won't spark, the electric spark control module might need to be replaced.
Replace the gas grill manifold
The manifold on a gas grill has the burner control valves and the connecting gas tubing. If the manifold fails, burners won't heat sufficiently or won't light at all. If a valve is stuck and not working, replace the valve. If the individual valve isn't available as a separate replacement part, replace the entire manifold.