I don't think its stiff due to friction, more to do with internal workings I reckon.
On good TRV the pin was actually loose when on hottest setting.
On faulty TRV the stiffness of pin does change with temperature adjustment but not in the same range
I have Myson 2 way TRVs on my radiators but there are 2 radiators that are not heating up.
All radiators have been bled and were previously balanced.
When I remove the plastic body of the trv from the radiator, the radiator will get piping hot very quickly so that side of things appears to...