I have an Atwood water heater model G6A-8E. When lighting, it fires up as long as the igniter is creating a spark. When the spark stops the gas valves close. I have tested for voltage on the upstream and dowstream sides of the ECO switch. I have 12 volts in both places. When the igniter stops the voltage goes to 0 closing the valves. I checked voltage coming to the unit it stays at 12 volts.

Water Heaters - RTO - Atwood Water Heater - 6 Gal LP