Mixer shower water temperature

[Tbone]

My mixer shower installed a few years ago has had to be gradually had the temperature increased on it just to keep it at the same useable temperature. I took it to bits to have a look but cant really see what to adjust.

Pictures are shown.
//www.diynot.com/network/Tbone/albums/

All help greatly appreciated.

Thanks

 

[LUNAT]

HI

order the cartridge (full kit)from plumb center WOLSLEY BRAND

 

[Tbone]

Hi,

Thanks for the reply - excuse my ignorance - is this a filter kit ? How would I get into it - ther eis no access from the rear of the shower - would I just remove the circlip etc and dismantle the shower from the front