Why do my hazards not flash when i open my 04 Ford Focus?

I bought an 04 Focus about 2 months ago which had a central locking problem at the time. The garage paid to fix this but now the hazards dont flash when i open the car but do when i double lock it. This used to work ok until i got the locking system fixed. Does anyone know what the problem could be? maybe something needs re-coding? Please help :-(