Test whether the altimeter works - open the altimeter screen and see whether the value changes when you climb. Check the settings to see whether it is not locked in the "barometer only" mode. Clean the sensor porthole by submerging the watch into a container with lukewarm water for a few minutes. Have a look on the About screen of the watch (menu » System » About), scroll down to the screen with components versions, and verify the SNS version. If it tells 0, then the watch is bricked. On some models you can try fixing it by reinstalling the firmware as described in this post) , on others it is not available and you will have to contact the Product Support through their website at https://support.garmin.com. Use the Phone or Chat options. Email exchanges take a lot of time.
