Honeywell wireless Doorbell (buzzer faulty, please read) (Camberley GU15)

Honeywell wireless doorbell with extension, but problem with buzzer button.
This is a set comprising of buzzer and two bells, one plug-in and one battery-operated, so you can have them in different rooms of your house. Both bells work just fine, in all modes. However there is something wrong with the buzzer button. It works intermittently but sometimes not at all or gets stuck. I have inserted a new battery (it takes a CR2032 coin battery) but it still happens. If you are happy to give it a go fixing/repairing the button please feel free. I have the manual/description with it if this helps.
Other options are:
Buying new buzzer button (they are available from Honeywell but after my experience with this one I wasn't keen to buy one)
If you happen to own a Honeywell doorbell yourself, you can use the two (working) bells as an extension to yours as they will be compatible with your buzzer.