Grohe SL rapid flush Internal wall system no longer flushing How to FIX

2 modes of operation dual flush (6/3l). For on-the-wall installations or studded walls. RAK Wall Hung Toilet Rimless Pan, Seat GROHE Concealed Cistern Frame WC Unit. GROHE 38772001 Concealed Cistern Frame 1.13m 3 in 1 Set.