scantronic 9449 when powered can't stop alarm sounding?

Alarm not been in use for sometime probably due to a fault. Recently the house power was shut off at the consumer unit. On reconnecting the alarm went off and would not respond to the punched in code. Only way to stop was to disconnect from the mains and disconnect the battery. All , assume only three fuses, tested OK. Do not know but is it possible the unit has defaulted the punched in code. Also the only indication to show on the keypad is "Power" when the mains are reapplied.