Garmin Fenix 8 update 23.39 leaves some watches without heart rate

Garmin Fenix 8 owners are reporting a fairly nasty problem after installing software 23.39, with the optical heart-rate sensor completely switching off on some watches. The update is now at 100% rollout, but for affected users this goes beyond a slightly wonky heart rate readings.

Version 23.39 was supposed to tidy up a number of problems and introduce some new features. However, for some Fenix 8 owners things didn’t go as planned.

The reports are not all identical, but the basic symptom is. Owners describe the green and red optical sensor LEDs going completely dark after the update, followed by the disappearance of heart-rate readings. That also knocks out measurements that depend on the optical sensor, including Pulse Ox and overnight HRV, while some users have reported missing sleep and Body Battery data as a result.

Restarting the watch may help, but not always

There is no clean fix at the moment. Some owners have managed to bring the sensors back to life by completely switching off the watch, leaving it off for at least 90 seconds and then restarting it.

A factory reset has also worked in a few cases. Although that is obviously not something most people will want to try as a troubleshooting step. Others say reinstalling the firmware or performing the extended shutdown made no difference.

There such reports from Fenix 8 owners, but the problem does not appear to be restricted to that model. Tactix 8 owners, for example, are also affected.

It is also worth pointing out that 23.39 may not be where the problem actually began. Similar complaints appeared with software 23.31 earlier in September. Garmin has acknowledged receiving reports of problems with 23.31 and had been recommending 23.39 as the newer software version to install.

This has been a messy run of Fenix 8 updates

Software 23.39 itself is a reasonably substantial release. It adds the “OK Garmin” voice wake phrase, a quick suggested running workout, indoor XC skiing and several Garmin Coach changes. It also fixes pace and speed dropouts, strength activity resets, Spotify problems and several other bugs.

We recently covered the broader Garmin feature update. That software brought hands-free voice controls and other additions to the Fenix 8 family. Garmin has also had to deal with several corrective Fenix releases this year. This includes software 22.44 following display complaints and an earlier Fenix 8 Pro update aimed at battery drain.

For now, there is not enough evidence to suggest owners should avoid 23.39 altogether. Garmin has completed the rollout and plenty of watches appear to be running it normally. But anyone who installs it and suddenly loses wrist heart rate should probably treat it as a software problem first rather than assuming the optical sensor has physically failed.