Fenix 5 Plus Altimeter has stopped working

You could check that the altimeter hole is not blocked, which I think is between the two buttons on the right hand side. 

I have checked it. It is clean.

Thanks

But it still doesn't work

I believe its the same problem I've been having. Floors don't show anymore and everything you start an activity it reverts back to 20000m and doesn't alter. I've heard that back dating the software helps but havnt had the chance to try it yet. Also i don't know where to find software version 17.30. Can anyone help? Try updating to the new 18.42 beta but that hasn't helped.

Update, I have tried to backdate after finding a version of 17.30 and problem persists

No idea. I have reset the watch too and no joy. Think it must be hardware as it doesn't look like a common problem

It's way off on activities and number of floors climbed. Only been doing it for last 3 weeks though. Guessing you didn't find a solution?

No solution. Was really hoping that it was a software problem and that an update would sort it but no updates for ages and my suspicion is it's a hardware problem as hardly anybody else is having the problem.

From what you describe, always altitude 20000 meters, that is most likely a hardware issue. To make sure, enter the service menu and have a look at the test mode/service menu (it is largely the same across the Fenix 5/6/7 line), and there is a pressure sensor test somewhere as far as I recall. Insane pressure or temperature values are indicative of sensor module failure.

I do not advice this, instead an out-of-warranty exchange may be a much better option, so do contact Garmin Support!, but replacing the sensor module is an option _if you have nothing to lose_. It may be glued in place, although that does not seem to be the case in the image here, and you can't assume the watch is still waterproof afterwards. Don't order a module/part unless you have checked inside the device what the exact part number is. Replacement parts can be expensive and they are often taken from used devices, sometimes sold untested. You need a backup device in case repair takes a long time, or in case you break the device further.