Just freed up another TRV tonight and thought I'd share. Most of my Peglar Terrier TRV's have now stuck open at some point - on removing the valve head the actuator pin appears stuck, and will not close despite applying quite heavy pressure. Discovered a while back if you slacken the inner brass nut which contains the pin, about half a turn thene pin frees itself. Simply retighten the nut and relace valve head and valve is fully operational again.