The pin is at the bottom of the screw up or down thermostat on a gas centrall heating radiator and is stuck. Have tried WD40, but no luck so far.

Donnie, May 2011

Take off control head and tap against the valve with the edge of a spanner. I am told that the protruding pin is "floating" and pulling up on it with pliers does not solve the problem - the piece below needs to be freed.

When the radiator begins to warm then you know you've fixed it - be sure the lock shield valve at the other end is open.

Peccavi, May 2011