Rad is leaking from TRV valve, seems to be seeping out of where the pin comes up. I tried tightening up the nut below the pin, but that didn't help. I then looked online and saw that removing the nut and packing with some plumbers tape may help, but whenever I try to remove the nut a load of water comes out constantly. I tried closing the lockshield valve, but still the same. From what I read online I should just be able to remove this nut, but maybe it is a different type of valve that you cannot do this. Picture of the nut attached for your perusal, the arrow shows the nut I was trying to remove...