We've just moved into a '30s house that has been recently (last few
years) extended and a new boiler. Some of the radiators appear to be off
but don't have a nice hand-rotatable jobby with marking from 0-9. How
safe is it to carefully try to rotate the spindle (where such a jobby
would be) with pliers?

At the other end of the rad there is another valve that typically one
does not appear to need to touch. These have a small white plastic cap
on, that can be removed or turned. What is this valve for? Can/should it
be turned and if so, does it have a stop or will it continue turning
until it comes off (as is, I assume, the case with the air-bleed screw
at the top of the rad)?

Thanks,

--
Tim

"That excessive bail ought not to be required, nor excessive fines
imposed, nor cruel and unusual punishments inflicted"

Bill of Rights 1689