surburban hot water tank pressure valve will not shut

Hey All, After getting the water system ready for season noticed the anode plug slightly leaking. tried to tighten gently but still leaking. Shut pump off and battery, opened up faucets in bathroom then tried to open release valve to relieve some pressure. It was very difficult and noticed it is very rusty. Loosened and removed anode while the water drained out from water tank. Anode head was all rusted too but rod was not too bad. Looked like one of those Camco versions. Removed old pipe tape and put new tape on and installed it and fill up hot water tank. Still leaked. Decided to replace anode with suburban brand. Installed anode this morning and filled the hot water tank up till hot water faucet started to run in bathroom. Shut hot water handle off and heard a lot of running water. Went out and saw the pressure relief valve just gushing out like a water hose?? The release valve does not seem to be closing? Should I just replace the pressure release valve? Looks like it is the 1998 original. P.S. never lit it up while doing this.