How can I mend my Scantronic 9800 intruder alarm?

My Scantronic 9800 intruder alarm was triggered by power being restored after a power cut. It initially showed an lb fault code after being silenced following me keying the code. At this point I switched off power to the alarm. However, I had to restore power to the alarm as I discovered the power to the immersion heater was fed from the same junction. The keypad is now showing an 5r fault code. Please explain what this means and how I may clear the error. Thank you,
Sheridan Roberts

Sheridan Roberts
November 2021