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[Help] Fenix 7X Sapphire Solar – Heart Rate Sensor Issues After Update (Both Optical & Chest Strap)

1490385

Hi everyone,
I’d really appreciate any help or insight on the issue I’m facing with my Fenix 7X Sapphire Solar. Apologies in advance for any language errors – English is not my first language.

What's the problem : 

After a recent firmware update, I started having serious problems with both the built-in heart rate sensor and my external chest strap sensor:

  • The optical HR sensor (wrist-based) is stuck and won’t show anything above 99 bpm, even during intense workouts (running, rowing, etc.).

  • The external chest strap (brand new) connects briefly, then disconnects after 2–3 seconds, even while idle. Sometimes, it won’t even be detected by the watch.

This is the second time I’ve had this exact issue. It also happened back in late 2024 with a Fenix 5X. I thought it was hardware-related, so I upgraded to the Fenix 7X — but the same thing started happening again.

At some point (before the last update), both sensors worked perfectly for weeks. But after the latest firmware, the problem returned — along with frequent Bluetooth disconnections from my phone, even when it’s less than 10 cm away.

 What I’ve Tried:

  • Factory reset

  • Reinstalling the firmware.

  • Re-pairing the external HRM

  • Testing with a brand new HRM strap

No improvement so far.

Even my old Fenix 5X now refuses to recognise the external sensors .

Has anyone experienced something similar?

Any advice would be greatly appreciated. This is really affecting my workouts and data tracking.

Thanks in advance for any help!

  • 0

    Which HRM strap exactly? Is it connected over BT or over ANT+. Does it use encryption (for example the new HRM 600 has this option)? Does the strap connect without problems to the phone? You can test it for example with the Strava app.

    I would also try disabling the BT and Wi-Fi on the phone, while testing the strap with the watch - it could help excluding that the problem is caused by an interference with the phone's BT/Wi-Fi.

  • 0 in reply to trux

    Thanks for your quick reply!
    Both HRM straps I’m using are low-cost Chinese models without encryption support. Still, they were working fine up until about a week ago. As I mentioned, the connection (whether via ANT+ or Bluetooth) drops very quickly—except during the HRV test, where it only disconnects after the test finishes.

    However, the built-in optical HR sensor has also started acting up. It now consistently shows low heart rate values for extended periods—for example, 93 bpm for 45 minutes straight.

    While I’ve had similar issues with the chest straps before, which were resolved after a previous firmware update, this is the first time I’ve experienced a malfunction with the internal HR sensor.

  • 0 in reply to 1490385

    As for the external HRM, first of all, I'd try replacing the battery in the strap, even if it still reports battery OK. And as I wrote, I'd test the strap with a phone, or with another device. And also try using an ECG gel (can be bought inexpensively in most pharmacies). Rince the strap thoroughly after each use, and hand-wash it frequently.

    As for the internal sensor, I cannot really comment since I do not own Fenix 7. Check the F7 forum for similar issues. If there are no massive complaints about it, then rather than a software problem, it could point to a hardware issue. In such case I'd contact the Product Support, and see what option they can offer.