kp5501z?

Is your keypad displaying a trouble message along with a lit trouble led?.

Ps: KP550 1Z is the keypad model (Focus LCD) not the make/model of the panel fitted,
Your panel is a DSC once used by ADT and British gas.

I'd suggest checking for a smoke/C'MOX detector located near by if the system isn't showing trouble warnings.

e manno
August 2013