Iphone 4s wifi connection problem

I'm using an iphone 4s on iOS 8.2 and I'm having problems with the wifi- it's connecting intermittently, and showing a greyed out button/slider at other times.

For example - I was using the internet this morning and all of a sudden the connection drops and the button is greyed out. A while later and the wifi connects again and now it's greyed out again.

The Bluetooth is still connecting fine, although I've recently had the wifi antenna replaced when both the wifi and Bluetooth fried.

I've tried resetting the network and the phone over the past few days that this problem has been happening and it's not solved the problem.

Is this still a wifi antenna problem, or something else?

Thank you in advance for any help!