This is my first post, so please bear with me.

Recently our power tripped out and for the first time since we have been in this new house (4 years) the alarm went off and would not stop by entering our code. In desparation, I removed the cover and pulled the mains wire out - together with the connection to the battery. The alarm stopped but when I reconnect either of these 2 wires, the alarm continues to sound and the key pad is unresponsive. Can anyone help?

Si

does the keypad light up??

and does the panel say anything else like tamper??

Yes the keypad did light up but I can't remember whether the tamper light was on. I'll try it again later and update.

you need an engineer i think

it sounds like the unit may have defaulted itself??

The battery was you first problem caused by not having your system regularly serviced, you now have a bigger problem that we cannot eally help you with remotely. Its unlikely the panel has defaulted due to the panel having an NVM but as James has said you really should call your installer.