My shower valve (older one in brass) was working fine with hot water except I had a little leak at the handle, I replace it by the mixer valve GP 77759 but not the pressure regulator GP 500520 because it is stuck inside and I cannot remove it.
The shower is working fine except the hot water is not hot enough.
Do you think it is the pressure regulator or the new mixer valve GP 77759?
Do you think I can find the 4 o rings to restore the old one in brass.
Thanks
Herve

Chances are you didn't set the Anti-Scald ring properly. Ring is located right under the handle. Remove handle, remove the ring, reinstall handle - and see if you get hot water again.

Back to you

Milo