Repair BT Diverse 4016 base unit?

The base unit for my BT Diverse 4016 has developed erratic behaviour. None of the handsets could contact it, and there was no ringtone. Switching off, waiting and switching on again restored it for a few minutes (with power on the charging pins) and then it died again. It's now been OK for an hour or so.

What is a likely cause of the problem? Can it be repaired, is it worth doping so, and where can it be done? I'm in South Bedfordshire.