Julie you probably have an intermitten tamper on your bell box outside, Its a common problem, you can link it out inside the control panel, this will prove that it is the bell box, then after a few weeks providing all is resolved your hubby can replace the box outside.
Scantronic make probably the best panels on the domestic and commercial market, so your in good hands. 
Regards Nick  07842 480037 Im in Kent
                
 Nick
                
 November 2009