Atwood t-stat (normal temp) controls the on/off firing of propane. It closes when water temp drops to 110*F allowing 12V DC to go thru ECO and to gas valve.
It OPENS to shut down propane firing at 140*F
The ECO t-stat (Energy Cut Off) is always CLOSED unless normal t-stat fails to OPEN and water temp goes HIGH.
It OPENS at 180*F shutting down propane firing and triggering the 'FAULT LIGHT'
IF ECO OPENS it will self reset when water temp drops below 150*F but 'Fault Light' can not be reset until switch is turned OFF then back ON.
Thermal Fuse (Clear tubing) connected to t-stat is a 'one time temp fuse'. IF it blows it has to be replaced. When it blows ALL 12V DC power is lost.....nothing will work until replaced.
It is a safety device that burns out at 190*F .....it is for flame blow-back out of combustion chamber/burner tube.
ECO and T-stat are both just snap disc devices BUT the terminal/spade connectors are different sizes. ECO larger. So the brown wires only fit the T-stat and the Red wires only fit on the ECO
ECO and T-stat connections need to be clean and tight
ECO and T-stat must be held tight against tank wall
12V DC goes to ECO and then to gas valve solenoids at same time High Voltage DC goes to spark electrode....DC will only remain on gas valve solenoids for 6-8 seconds unless main flame lights off and proves it lit via milivolt signal back to circuit board.
Normal T-stat (small terminals).......Opens at 140*F (controls firing and water temp between 110*F to 140*F)
ECO T-stat (larger terminals)..........Opens at 180*F (always closed unless temp goes too high)
Thermal Fuse (small terminals)........Burns out at 190*F (No DC for anything if it blows)
