On Wed, 25 Sep 2019 05:48:33 -0700 (PDT), "Tim+"
wrote:

Although the pins move up and down I think sometimes the sealing washer sticks to the seat.

A sharp rap to the side of the valve body with a small hammer can sometimes shock the jumper off its seat but this is only a temporary repair once its started sticking in my experience.

It's the valve head. Take it off and the radiator works. As in my OP
I think the central column is not moving as it should.

--
AnthonyL

Why do scientists need to BELIEVE in anything?