Just setup a new server and have installed mod_pagespeed.

It only seems to be working on html pages, not PHP. Below are the headers for two simple pages and apart from the Vary: Accept-Encoding I can't see any differences. Can anyone help me to get this working?

Below is a php page where you can see pagespeed is not working

HTTP/1.1 200 OK
Date: Thu, 29 Sep 2016 09:20:35 GMT
Content-Type: text/html;charset=UTF-8
Connection: keep-alive
Set-Cookie: __cfduid=d160aaa9e45a863e3a570263393bd44d41475140835; expires=Fri, 29-Sep-17 09:20:35 GMT; path=/; domain=.thinkoptimised.com; HttpOnly
Set-Cookie: grav-site-40d1b2d=eo47rrkp2bv5vo91fn8gjjqbs0; expires=Thu, 29-Sep-2016 09:50:35 GMT; Max-Age=1800; path=/; domain=www.thinkoptimised.com
Expires: Thu, 06 Oct 2016 09:20:35 GMT
Cache-Control: max-age=604800
Pragma: no-cache
Set-Cookie: grav-site-40d1b2d=eo47rrkp2bv5vo91fn8gjjqbs0; expires=Thu, 29-Sep-2016 09:50:35 GMT; Max-Age=1800; path=/; domain=www.thinkoptimised.com; HttpOnly
Content-Encoding: none
Server: cloudflare-nginx
CF-RAY: 2e9e5c2f16de1359-LHR

Below is the html page where you can see pagespeed is working

HTTP/1.1 200 OK
Date: Thu, 29 Sep 2016 09:21:20 GMT
Content-Type: text/html; charset=utf-8
Connection: keep-alive
Set-Cookie: __cfduid=dac868428de03c5593734cc0f9972f9421475140880; expires=Fri, 29-Sep-17 09:21:20 GMT; path=/; domain=.thinkoptimised.com; HttpOnly
Vary: Accept-Encoding
X-Mod-Pagespeed: 1.11.33.2-0
Cache-Control: max-age=0, no-cache
Server: cloudflare-nginx
CF-RAY: 2e9e5d4626f40a66-LHR