RV Repair: hot water heater, water heater valves, hot water heater

Question
I have an atwood gas hotwater heater in a 1988 Terry. I'm pretty sure it is the original hot water heater. I noticed this past w/e that water was pouring out of my releif valve and the flame was still on heating the water. I don't know if the heater kept running because the water was blowing thru the  relief valve and the heater was trying to keep up and I need a new relief valve or the system overpressured  because the heater would not shut off when the water reached the right temp.I appreciate any help you can give me.

Answer
Hi Kevin:
I think you analysed the heater correctly. The heater is either running past the two safety thermostats or the pressure relief valve is bad. If you have a manual system, that is the gas valve is the only control and you light it manually then I would first change the relief valve. The valves are standard water heater valves available at most hardware stores for about $12. If that does not fix it then change the gas valve, about $90-$120. If it is an electronic control, one where you just turn on a switch in the trailer to start the heater, then also change the relief valve first and then change the thermostats. There are two, under a black cover ouside. One disconnects the power to the control box at about 140 degrees and the second disconnects the gas valve power at about 190 degrees. They come as a set for about $37. Good luck.
Bill