By default HSTS is disbaled because few customers still accessed 
http://links 
from 
https://pages 
for same domain so this option is not enabled by default. To enable it follow next steps

1. open/edit(create) with Notepad **\Clients\webserver\settings.bin 

2. and add/save as last line
enable_hsts_https=true

3. restart HTML5 via AdmintTool GUI

4. now in **\Clients\webserver\web_log.txt you should see following message Enabled HSTS HTTPS header! indicating that the HSTS was activated.

As in notation above remember, after activating HSTS you won't be able anymore to access http links from your page.