I have a Rheem 41V40, 50 gallon, gas hot water heater in our house - not sure how long it has been here - the serial number is 0502 103535. I got in the habit of turning the water off at the street when I leave for a trip any longer than a few days - it's older house, and I felt that this would minimize any water damage from a busted clothes washer line or broken water heater.
I came home this evening after being gone for 5 days, turned the water back on at the street, and the pressure relief valve for the hot water heater tripped - it's got a pipe that vents the water to the outside of the house. It stayed tripped for a few minutes (I was outside), until I got back inside and I reset the tripped valve, and things seemed fine. I could hear the tank heating, and I assumed that was because of the cold water that came into the tank when it was venting.
There's a 25x25 inch catch pan under the water heater - I guess to catch any water that leaks from the hot water heater and drain the leak to the outside through a drain pipe running out of the back of the drain pan, which ties into the pipe that the pressure relief valve uses to exit its water to the outside - between where the drain pipe comes out of the catch pan and it connects in to the pipe that services the pressure relief valve, there appears to be some kind of valve or device in that section of pipe - it looks like maybe it's supposed to prevent the pressure relief outflow water from flowing back through the drain pipe into the drain pan, instead of going outside where it's supposed to go - I'd never seen anything like that before and I couldn't see it clearly.
Now I notice that the drain pan under the water heater has a small amount of water in it - maybe a half of a small glass. The tank has refilled and reheated - there's no water on the outside of the tank, no water dripping, and no water near the pressure relief valve at the top of the tank.
Did this small amount of water in the drain pan most likely come back through that valve in the drain pipe? Or is it most likely something else and what's the fix?
Thanks very much for your guidance.