Clean the burner tube and clean or replace the orifice if the spark is present but there is no gas. Tighten the wires, replace the ECO or replace the circuit board.
Secure the wires to the circuit board and clean the electrodes if gas is present but there is no spark. Reset the spark gap to 1/8-inch. If this doesn't work replace the electrodes or circuit board.
Put the valves in the proper position if there are bad water temperatures. Reset the thermostat if that doesn't work.
Replace the gas supply is there is an erratic flame. Adjust the valve and main burner alignment. Clean the orifice, main burner and "U" tube as well. Be sure there are no obstructions.
Clean the edge connector if there is no spark or gas. Clean the edge connector, replace the thermal cut off or replace the switch. In the worst case situation you may need to replace the circuit board and thermostat.
Replace the spark electrode and thermostat if the intermittent fails to ignite. You can also try tightening the ground screws.
