Project "Replace Pressure Release Valve" was a complete fail

IF you go the heat route.......

Remove the tstat rubber cover
Remove both sets of t-stats
Pull the 120V and 12V wiring inside over to the left as much as possible away from heat


I prefer some penetrating oil, some taps with wrench/hammer just to jar it so penetrating oil can seep between thread, let soak for at least an hour ----couple shots of oil/whacks while waiting
Then try to 'tighten' it a bit before trying to loosen

A 'cheater pipe' may need to be part of the equation of removal.