Sparky I could get my meter probes onto the switch terminals and saw the reading go to zero ohms when the switch was pressed. If entering the engineers code should reset the alarm then I agree, the board must be faulty. thanks for your help.
After entering the code I used the 'B' & 'NO' buttons to scroll up and down the menu but I cannot identify how to restore. One of the options uses the reference 'UDL' and don't know what that's about. I have disengaged the output with the faulty sensor. Not touched any inputs.