If it’s off in the thousands, it’s likely your altimeter is broken. I recently contacted garmin and they are sending me a replacement.

^^^^^This.

If it just reads a constant value that is waaaay out of range, the alt/temp sensor has died. It's a known weakness of some Garmin watches (I'm on my 2nd warranty replacement Fenix5 for this issue). Hopefully you are still in warranty; if so Garmin is pretty good about sending you a refurb as a replacement.

Lots of threads on this. Ex: https://forum.slowtwitch.com/...20altimeter#p7279589

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

My 935 has been that way for years. I just update elevation with Strava data.

I can't believe how many watched they replace for altimeters. Can't be cheaper than using more reliable components or thinking of an alternative way to provide elevation data.

I wish there was a way in Strava/Garmin Connect/Training Peaks to just ignore the device altimeter data, or a way for Garmin to make the Temp/Alt sensor optional. I would buy a new watch today if I could get a Fenix or 9x5 without it. I'm holding off buying a new one precisely because of this issue.

*Every* Garmin I've had with an altimeter has failed. It's a pain in the butt to replace it and reset-up all of the custom screens, re-pair all of the ANT and BLE devices, and eventually you get out of warranty.

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I ride Felt.

Only 2 types of Garmin watches. Those where the altimeter has failed and those where the altimeter will fail. They know it. They do nothing to fix it. Once it's out of warranty you are scr#@d.

I am hoping the Forerunner 945 LTE might have an improved altimeter. I would also like to see the HRM monitor not drown.

You can turn it off in Garmin Connect, and on Strava. When you select "enable" elevation correction, it takes the data off a topographical map and doesn't use the electronic altimeter. But you will need to do this after each activity. So it's still a pain. And the use of topographical maps have their own idiosyncrasies. Garmin does make some units that only get elevation via GPS. But these are typically not targeted towards athletes.