Almost certainly water ingress causing the fault. Unless the engineer has changed a device and incorrectly addressed it.
The lifetime of Smoke detectors depends on the environment. A stable dust-free environment the detectors can last well over 10 years. My advice would be to replace any fire &...
Siren replacement during a maintenance visit approx £75?? Gotta be worth having new imo. 16 year old siren that has tamper switches exposed to extreme weather just not worth the gamble.
In my opinion Pyronix is the best system. Hundreds of threads on this forum alone and any questions normally get answered so there should be no need for their technical support.
I think it is a known fault from about 2 years ago that if you change the batteries the siren becomes faulty. Hope not been I’ve certainly read about it before.