If it is one with the soft touch membrane panel it could be the contacts within the panel are poor. Its easy to remove the top membrane and access the pcb and contacts. I used electrical contact cleaner and some very fine emery and after replacing the pccb as an additional measure sprayed a coat of pcb lacquer. Never had problem again. Sometime the wiring in the flush tank compartment can become corroded so clean the joints too. Helpful videos on Youtube.