I've had an 800 for a couple months now and it's always worked perfectly, then over the weekend I moved across town, and my last two rides, the elevation profile has looked like this:

https://connect.garmin.com/activity/229099738

https://connect.garmin.com/activity/229428263

For reference, the first ride has about 500-1000 feet of climbing and the 2nd ride probably actually has about 1500-2000 feet of climbing. I don't understand what's going on here. Can anyone help?

First, try resetting the unit and seeing if that does the trick. To do that:

To perform the master reset:

1. Power device off
2. Press and hold Lap/Reset and Start/Stop
3. Power device on while still holding both buttons
4. Continue holding buttons when the Garmin "splash" screen appears
5. Release buttons when Garmin "splash" screen disappears

The Edge 800 is now reset. Leave the device outside with a clear view of the sky for a minimum of 20 minutes to acquire satellite data.

It may not solve your problem, but is the recommended initial solution.

Do you have a saved location near your ride start? A location can be saved, with a manually entered elevation. That might cause the starting elevation to be way off.
see page 25-27
https://www.manualowl.com/m/Garmin/Ed...133444?page=29

Like what rm-rf said, you need to set an elevation point for your front door step or wherever you start your ride so it has a good reference point for the weather that day.

Link to manual placed in post above did not work for me (404 error page).
Theres some backup link if someone will need it Garmin Edge 800 User Manual - Page: 2