Red light stays on 1 of the PIR's (Veritas 8 system)?

Hello
Hope someone can please help. We have recently moved house and there is a Veritas 8 alarm system fitted. I have recently changed the battery as that was well out of date, so all the correct lights are now on the main box, but when I try to set the alarm, zone 2 red light appears on the main panel. I checked the PIR's in zone 2 and 1 of them has the red detector light staying on. Should I purchase a new PIR, would it be faulty or is there another possibility before I buy a new 1 ?

Thanking you in advance