If you decide to pull the burners you can purge the line at the same time. To get the burners out you need to undo the union in the gas line. This is either in the heater to the left of the gas valve or just outside the heater.
On the Laars there are some screws holding the burner assembly in place. If you're lucky someone has already removed them and not bothered to put them back. They can be a pain to get out.
Once the burner assembly is out, you remove each burner. They pull right out. You will see a burner orifice for each burner. They thread out. Once out you can see if there are webs in there. Clean them out and reinstall.
For purging you don't need it flowing through the gas valve. Purging out of the union you have open is usually fine.