Great Tit Nest in my urban garden has gone quiet

We first noticed about a week ago that our nest box (bought from RSPB online shop) was at last occupied after three years of being ignored. We could hear chirping and noticed the parent birds flying in to feed the chicks. Unfortunately the only place to site the box was by our back door. We have tried not to disturb them but I'm now very concerned we have frightened the parent birds away. it's been two days without any activity or noise from the box. What is the likelihood that human activity (we only go outside once a day) has driven them away? Is it possible that the chicks have fledged? I'm hoping that the chicks were there longer than a week and we just hadn't noticed. There has been a lot of rain which I hope hasn't affected the parent birds' ability to feed their young, although for the past five days it's been sunny. Hoping for reassurance!