Fenix 7 with System Software 15.77 shows Temperature "--------" on watch and 0 Celsius in activities.

Are you talking about the internal temperature sensor or the weather temperature?  If the former, it could be a faulty sensor and would suggest you try a hard reset (push and hold down the light button until the watch switches off).  A faulty temperature sensor can also impact the barometric and altitude values.  A useful widget (at least I find it useful) is PSX-* Raw Data.  This allows you to scroll through the various watch sensor values to see what is being reported.

Michael, you are correct, during rides the altimeter added a fair bit of elevation, which my Edge cycle computer did not match of course. So other measures are also affected.

My experience with Garmin was extremely positive on this one.

My past experience with the Fenix:

       * 1st: Fenix 3 (I gave it away.. I duuuhhhh).

       ** 2nd: Fenix 5 - barometer failed

       ** 3rd: Fenix 5 - altimeter failed (to be fair I did had a bad bike fall but the 2 events did not coincide, the watch survived the fall but failed some months later)

       ** 4th: Fenix 7 (this one)

       ** 5th: Descent Mk2 (for diving)

My use case:

       ** I love the morning report (it changed my “less than ideal” sleeping patterns for the better)

       ** Measure swims

       ** Measure runs

       ** Measure rides

       ** Measure some 70.3s and some marathons

       ** See phone notifications

I have no interest or used any other features on it such as GarminPay, touch screen, Spotify, music etc. They are all disabled or not configured. Having said that, the watch does not leave my wrist.

So with the above, and your useful information about other measurements being affected, I took the less than 2 year old watch to the local Garmin distributor who:

       ** Confirmed the failed temp sensor

       ** Confirmed that other measurements are affected since the sensors are highly integrated

       ** Replaced the watch at no cost and extended the warrantee by 3 more months

They also explained the following how to care for your watch:

       ** Don’t use high power USB sockets

       ** Don’t charge overnight

       ** Don’t wear the watch during sauna, spa, etc. (which I don’t do) i.e. places where you might get internal condensation

Would like to thank Garmin for the hassle free engagement, and Michael for his informative response.

Hope the above helps others.