MH17

Hi, Just moved into a new home, the previous owners haven't even given us some keys so not a great handover. There's a veritas R8 alarm system that's off at the consumer unit. We've got five sensors in Hall, Landing, Kitchen, Living room, Dining room. We turned on the alarm at the consumer unit the other day and punched in the default user code followed by the default engineer code and the zone lights came on on the keypad. We tried to do a walk through test but it doesn't work as the online instructions suggest. The battery in the control panel is 22 years old so we're gonna change that but just wondering if anyone had any advice? One of the sensors doesn't light up - is it likely it's just broken? Just after any information from anyone with experience. Should we just upgrade the system?