The ballcock in the supply tank in the loft has been dripping and causes the tank to overflow. It's thick will limescale too so I bought a new valve and float to replace it.

Access to the tank is severely restricted and I can't get my head in to see what I'm doing. I can reach over and managed to remove the pin and float arm. With an adjustable spanner I have located the nut on the valve and turned it many times but it doesn't seem to be coming off.

Should I be gripping something else as I turn the nut on the valve? Or should I be unscrewing the nut on the outside of the tank instead?

Just so happens I recently had to complete the exact same job in our loft.

You'll need to unscrew the nut on the outside of the tank which joins to the mains - should be fibre washer in the nut - if you can't remove the washer in one peice you'll need a replacement to fitt the new ballcock.

Next you undo the nut on the outside of the tank, this compresses the ballcock fitting into the plastic wall....when I refitted the new ballcock a few turns of PTFE tape on the thread made for a good watertight seal.

_________________
Don't buy a dwarf with learning difficulties,
It's not big and it's not clever.

OK, sorted thanks. I did try to remove that nut initially but it wouldn't budge so thought I'd better check.