Scantronic 9448+ goes off before fully set?

Following a power cut in the village the alarm triggered. When the power came back the alarm was reset using the key pad. Since then although the system shows normal on keypad, on setting alarm the system begins to set as normal. However about half way through the setting time of 30 seconds the internal sounder goes off and zones 5 & 6 flash red (these are unused zones) on the keypad. Thereafter the system will not activate the outside sounder even if any of the in-use zones are triggered. Entering code twice resets the system. Is there such a thing as a master/maintenace re-set. Have checked internal box and key pad - all seem OK visually.