Firstly turn the supplies off to the shower,remove the thermo shower body and check the in-lets for dirt,debrior lime scale if your'e in hard water area,your in-let may have a fillter on them,you can flush these out under a tap,and replace the shower body and test.
hope this helps good luck
p.s it shouldn't matter if your shower cost you alot or little when it's working your not standing there thinking i'm under my shower i bought for X amount so don't go spending out just yet!!
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