Kia ora, 

Our blue RCD keeps have been tripping about twice over the past two weeks. The house itself is about ten years old so the switch would be around that age. 

I've isolated it to be the plugs within or kitchen, about three plugs. So as soon as that black power fuse gets switched back on, the RCD would trip again. 

However, even though if I've unplugged the appliances from the switches involved and switched off the plugs, the RCD would still trip. 

This usually resolves itself after about an hour or two. 

I've been told that this is possibly a faulty fuse box/RCD box. 

Any suggestions or ideas the cost to replace the box if that's the issue?