NCLeeds

The RCD in our fuse box tripped, not due to the alarm, but switching off the alarm circuit in the process. When I sorted the RCD, the alarm box was beeping so in the end I just turned off the circuit and we went without an alarm for a while. I'm now getting around to sorting it. I've replaced the battery and it seems to work as expected when setting: enter code, press FULL, hear the usual beeps. But it doesn't stop beeping when I enter the code again. It only stops when I enter the engineer code, or when I press RESET. I've reached the end of my knowledge (not hard!) on this. Any ideas?