Your question seems only to common one, inside the processor ie the mixer valve there are two rubbers with spring inserts inside which sit in two ports easy to change but problem comes has to were to obtain them you may also wish to check the pressure out put of combi incase its to high Pressure valves may be required , the only intrest Aqualisa show is to sell you a new processor I contacted the shower doctor on line and await to if there or where I can get replacements good luck.
Ray friend in need
July 2010