Keep-Alive problem

I've been trying to get KeepAlive working. The following is set in my httpd.conf. . .

KeepAlive On MaxKeepAliveRequests 100 KeepAliveTimeout 15

But it's not working, keep alive is being sent as 'close' or no keep alive header sent at all. If I try adding the following to a virtual host. . .

Header set Connection keep-alive

That makes the website send a keep alive header, but it is appended with 'close' immediately afterwards i.e. both keep-alive and close are being sent together.

This is fresh install of Centos 7. Please help!