Ruud Gas Hot Water Heater Shuts Off

If this is a hot water heating system for home heating It may be thermocouple of flame sensor. If it has a sensor rod in the flame check and make sure flame is hitting it. Also a little sand cloth to polish it may do the trick. I have to due this to my gas furnace sensor every couple of years. If this unit has a pilot light and it is weak and yellow verses strong and blue it may need cleaned. Some times you can tap on it while it is burning and it will dislodge plug. If it A domestic hot water heater for washing and such the above still holds true. If polit is strong and hitting thermocouple then replace thermocouple.

Sounds as though your thermostat isat fault.,