Recently when my hot water heater is heating up I hear a release valve go off and water pour out of discharge tube, but its not the pressure relief valve attached to the hot water heater there another one it seems on hot water line leaving the hot water heater. What's the second one for? Does it just need to be replaced.

There should be only one T&P valve, a picture might help

Yes I agree with Bob a picture will help, Thanks.

John

I don't know what they are specifically called, but I have seen small valves mounted on the hot piping side. My son's old HW heater had one, on the hot side, connected through a Grundfos circulating pump. I removed the non operable pump and the valve. Looks like a mini TPV valve.

If that pressure valve goes off that may indicate you have either High Pressure or Water Temperature is too high. Please, check out your pressure and w/h temperature setting first before you start removing or capping off anything on or around your hot water heater .

You really need only one Pressure Relieve valve. If there is one fully functioning PRV installed on the body of your water heater than that should be the one should leave. The other one, installed on Hot Water pipe leaving your water heater, you can remove.

Milo