Help Please - How to get this apart!

[cockneycob]

This shower thermo mixer is dripping from the central shaft. I do not know quite how to get it off. I am thinking that there is an 'O' ring in there somewhere that can be changed. The picture shows a grub screw that is half recessed behind the big nut shaped thingy. Any advice would be appreciated.

 

[Puddle]

This shower thermo mixer is dripping from the central shaft. I do not know quite how to get it off. I am thinking that there is an 'O' ring in there somewhere that can be changed. The picture shows a grub screw that is half recessed behind the big nut shaped thingy. Any advice would be appreciated.

Well isolate the water to the shower unit

Then undo the big nut shaped thingy with an adjusting spanny thing or grippy whatsits and then you will have access to themy thingy guby screw and not one put several 'o' ringys

ps take a shower first coz could be off a while