Flashing Power LED but not in Test Mode?

[DIYdonut81]

I have a very old Wickes 710712 wireless 418MHz system that has been pretty reliable for nearly 17 years now. I think this was a branded Yale/Response panel?
Normally the power LED is a steady green, but when you switch it into Test Mode, the green LED flashes. Recently, the green LED continues to flash even when it's not in Test Mode (I know that the system is definitely out of Test Mode because otherwise the detectors would trigger the alarm pulse when I walked past them).
I've tried powering it down (both from the mains, and by disconnecting the rechargeable battery in the control panel), but this does not clear the fault.
The alarm otherwise functions as normal, but I wondered if there is a cure for this, or is it just something I should ignore?

 

[sparkymarka]

Ever changed the battery in the control panel ? What happens if you turn the mains off for a couple of hours does the panel still work ?

 

[DIYdonut81]

Yes, the battery was not holding much charge when I opened the control panel and removed it, so it has been replaced with a new 1.2mA 12V battery, as has the 6V one in the siren unit. I have also replaced every battery in the PIR' and door contact sensors.