My hot water tank cold water is always flowing and it's losing water out of the temperature valve relief tube on the cold water intake side (see attached photos). I just noticed this, but it could have been going on for weeks. The tank natural gas and is 10 years old and I've never tested the TP valve until recently. I've never pulled the TP valve out to check it. I've tested the thermostat and the burner is firing fine. We have no problems with the hot water in the house. The house water pressure is sitting at around 60psi
Home Depot guy said that the pressure in the city has gone up due to check valves being installed, however I'm not so sure. He said to install an expansion tank on the cold water intake side, however, I'd like to understand what the problem is better before doing this. Another potential clue is that there was a broken water main at a house down the street, however, I don't think that this is contributing to the problem as our house pressure is 60 psi.
Is this pressure, temperature, tank related, or perhaps a failed temperature control valve problem (on the cold water intake)?
What should I do to better diagnose this problem? Should I replace the temperature control valve on the cold water intake? Install a expansion tank? If so where would I install the expansion tank on my cold water side?
edit: That "temperature control valve" is actually a thermal expansion valve.
From the website: https://www.mmcontrol.com/apollovalves/plumbing.php
Apollo® 78RV Series Combination Water Heater Isolation Valve/ IAPMO approved Thermal Expansion Relief Device. This combination water heater shutoff and thermal expansion relief valve is an ideal alternative to expansion tanks in residential plumbing systems.
Update 2: I have run the cold and hot water tests for both at 5 minutes each and neither have stopped the flow of water out of the thermal relief valve. When I closed the valve completely, the water still flowed, however it turned to hot water after around 3-4 minutes. Does this mean I have too much pressure inside the tank? Replace valve? Install expansion tank? Replace water heater? Call in the pros? :) Many thanks again all.
Please see attached photos for details.