Removing a thermostatic cartridge

[dw2014]

Hi, can anyone help please? I'm trying to remove the thermostatic cartridge to check the model type to buy a replacement. Below is a photo of where I am now. I can't remove the bottom chrome cuff. I can turn it but it doesn't loosen. I think I need to remove this in order to take the cartridge out? Any advice would be much appreciated. Many thanks!

 

[SimonG]

Send the photo to shower doctor. Search online.

 

[jtsplumbing]

Large brass nut at back, Have you tried to undo it ? it could be a left hand thread.

 

[rocketmanbkk]

Call a plumber.