Stuart,
Firstly try disconnecting the mains power and battery, leave for a few seconds then reconnect,
once powered up enter your code,if your code does'nt work use 0123.
If its still showing a tamper fault then follow the instructions below.
a simple way of bypassing the tamper fault is to link out the tamper zone with a piece of wire , not forgetting to link out terminals T & A (tamper return & 0 volts)
Once linked press in the tamper spring, the panel should go back to normal operation.
Let go of the tamper spring and enter your code.
If that doesn't work disconnect battery & mains power ,link out all zones and tamper circuits, link terminals 13 & 23 (PA & SET) then power up, after a bleep your panel will be reset back to factory settings.
You will then need the engineers manual to reprogram.
Send me an email and i will send you one (its of an XM4 but the programmings the same)
Johnny_two_bob@yahoo.co.uk
johnny2bob, April 2007