Hi Graham.
You will need the user pin code and engineer code to reprogram the Melcom. By default these are 1234 and 9999 respectively. If you don't know the codes you can factory reset the unit by removing the cover and shorting out the NV RAM pins to the right of the circuit board next to the keypad. Next, remove power by disconnecting the battery and the mains. After 30 seconds, reapply the power and remove the short on the NV RAM pins. The codes (and all other programming) will now be back to the factory defaults.
Regards,
David.
David Savery
February 2010