Hello, let me start by apologizing for the length of this post. I am new to RVing and want to make sure I get all the info out there. A few weeks ago I purchased a 95 Fleetwood Mallard. On the sales walk through we noted that the Atwood G6A7 water heater would not light. They had their tech look at it and he determined it needed a new gas valve (Atwood 91602) So they installed a new one and we made the deal. About a week later I was staying in the trailer so I lit the water heater with no issues and took my very hot shower. The thermostat was set at max. The next day I had no hot water so I figured the pilot had gone out. Went out back and lit the pilot but it wood not stay lit after holding the button for over a minute. The next day I called the dealer and she sent a service tech out. First he cleaned the burner burner tube and the pilot orifice. Still nothing so he changed the thermo coupling and still nothing. He then determined it needed another new gas valve. At this point the dealer said they didn't make enough money on the deal to warranty the gas valve they had installed.
When the gas valve is replaced has the pilot orifice been replaced as well? If the pilot orifice has been damaged/is too large it will cause the ECO to trip and as the previous poster mentioned the Atwood ECO switch is a one time use device and the entire valve needs to be replaced when it trips. I also noted that you said you had the thermostat at Max ... while in theory this shouldn't impact the ECO switch I suspect there is a risk with the thermostat at Max that you could be getting the water hot enough to burn out the ECO in the thermostat. I would recommend replacing the pilot orifice and gas valve and verifying that the pilot is not excessively high and also not operating the heater with the thermostat on max.
That is the valve used both times and the water heater was full before being lit. Just to clarify on both valves I waited until the water heater was done heating before getting in the shower and both times the water heater was running again when I got out of the shower. Did not notice failures until next day.