Bristan bar shower temp control

[Fizza]

Morning all the temp control on the left hand side its quite difficult to move. I can do it but the kids struggle. Is there any lubricant which can make it easier to turn. Is this caused by lime scale. If i needed to take the cartridge out is there a recommended spanner/ tool for this

Thank you

 

[Exedon]

There are quite a few bristan bar mixers if you have lost paperwork have a look on bristan website to see if you can identify it.
If its one of the 'cost effective ' mixers course be simpler to change whole thing and get a 5 year warranty.
Literally a 5 min job to swap.

 

[gas112]

Just as cheap to change the whole bar get them for 50 quid at screw fix etc and takes 5 mins