If the systems stability was ok before you renewed the pir, then you have incorrecty wired it,or it could be another device on that zone that has failed.
A coincidence I know,but it does happen.
if you are utilising the two core cable,then that's doesn't count,however connection security does.
Is it possible you have fitted a none pet tolerant pir... got any pets....to a pet tolerant pir system?.
If you can rule these factors out,have you set the pulse count to minimize detection of environmental disturbances?.
Change it from setting 1 to 2/4.
Setting 1 can be a little sensitive for a living room,especially if it on the small side.
no name
February 2012