We've had several readers contact us to say they can't connect to WhatsApp. For many the problem was with the service itself, and has now been rectified. However, if WhatsApp is not down, and you fear the fault lies with your own phone, here are some suggested fixes you can try. 

If you can't connect to WhatsApp, this is usually because you don't have an active internet connection. Check whether you can use any other online services or browse any web pages on your phone.  
If you can't get online at all there are several things you can try. If you're using Wi-Fi, first try toggling the connection on and off, or putting into and then removing the phone from Flight mode. Alternatively, you can try restarting your phone.  
Also make sure your phone isn't dropping the Wi-Fi connection when it goes to sleep (go to Settings, Wi-Fi, choose Advanced from the Options menu, then ensure 'Keep Wi-Fi on during sleep' is set to Always). 
If you're sure the broadband service itself is not down (downdetector.co.uk is a good place to check), you could also try restarting your wireless router. 
If you're using mobile data then check your mobile data connection is not turned off in the Settings menu, and that you have sufficient signal.  
You should also check you haven't restricted background data usage for WhatsApp in the Data Usage menu, and that your APN settings are correctly configured. If you can use WhatsApp over Wi-Fi but not your mobile connection, it's likely that the APN settings are not configured to allow non-web traffic - check with your mobile operator. 
If you're happy that you have an active internet connection, the next step is to ensure you have downloaded the latest updates for WhatsApp.  
On an Android phone you should check for app updates by opening Google Play, tapping the three lines at the top left and choosing My apps, then checking the Installed tab for available updates. On an iPhone open the App Store and tap the Updates icon at the bottom right of the screen. 
If WhatsApp still isn't working, try uninstalling and reinstalling WhatsApp. You will lose any conversations you have, but you can back these up by opening the Settings menu within WhatsApp and choosing Preferences, Backup conversations. 
On an iPhone WhatsApp suggests that you also make sure you are running the latest version of iOS.