I have discovered that after replacing the thermocouple has been tried, that
the valve itself on this unit must be changed. It's a 19 year old Empire
RH-340-3V5. There's a place nearby that has a generic valve that will
replace this one, they say, and it's not too expensive to consider.

So, I'm trying to save a few bucks, and at least remove the old valve to
take it down to the parts/service place. I'm at the point where there is
just the manifold pipe still in the valve unit - everything else is
disconnected. I don't know where I'm supposed to disconnect it. Does the
pipe come off the valve altogether? Is there a screw on the valve body for
this?

Or do I try to take the whole manifold pipe off?

I have tried to crank the valve around with my hands, but the pipe is in
there pretty good, so they didn't budge. The pipe is just threaded on that
end, into the valve body. There is a what looks like a bolt or pin nearby
the entrypoint of the pipe on the valve labelled "PRESS TAP".

TIA -
Mark