1.Place thermostat in the right cutou(as you face the water heater). 2.Replace spring and washer behind metal tabs on water heater combustion pan to hold thermostat against water heater tank. 3.Cover with black foam cover (provided with kit). 4.Reconnect brown wires to thermostat and red wires to ECO. 5.Turn unit on.
https://www.amazon.com/Thermostat-Assembly-Replace-Replacement-Emergency/dp/B07QR85Q1T