The vibrate mode on my phone will not work My phone will not vibrate on vibrate mode. It will not vibrate on the sound mode (which is what I have it set on). When i get a text or notification it has to be on full volume to make a sound or silent. It will not vibrate at all, not for a call or for a text. and my phone is HTC desire 810
How to fix vibrate in my samsung galaxy phone

Remove the battery from your phone for 30 seconds and then re-insert it before powering the device back on.

check, first if this issue is caused by a third party app installed in your phone by starting your device in Safe Mode. Once in this mode observe your phone and see if the vibrate changes on its own. If it doesn’t then the problem is most likely caused by a third party app installed in your phone. Find out what app this is and uninstall it.

Factory reset your device but be aware that this will wipe all user data such as your contacts, photos, app data, etc. Make sure you backup first.

If the problem persists, it means that the microphone is damaged. You should take your device to a repair shop to get it fixed or replaced.

Source - http://www.gogorapid.com/how-to-fix-vibrate-not-working/