Beware Garmin customers that own, or are thinking about buying, any of the products containing the optical heart rate sensor.  I have now owned three Garmin products with the wrist-style sensor (Vivoactive HR, 735xt and the 935xt).  All of the devices displayed some level of this plastic warping defect.  Here is a picture of my older 735 with the defect.

The first watch I owned with an optical HR sensor was the Vivoactive HR.  After about six months it started to warp.  A month later the sensor failed to be able to read an accurate HR.  At the time I thought I must have dropped it or damaged it during use.  I then purchased the 735xt as both an upgrade and fix.

After three months with the 735, I noticed the issue with the new watch.  I watched over the course of the next 30 days as the warping got worse, to the point the sensor stopped reading.

Here is the biggest issue for Garmin consumers.  When I contacted them, they advised that the watch is only covered under a 90-day warranty.  I was about two week outside of that window.  I would have had to have paid $150 to obtain a new refurbished unit.

So, I then bought a 935, thinking the more sunk-in design of the sensor would fix the problem.  I purchased the 935 at the end of September 2017.  Today, at the end of March 2018, the watch is demonstrating the same sensor warping issued the other two watches did.  Here is what it looks like:

Garmin Forerunner 935xt with optical HR sensor warping.

I’ve again contacted Garmin about the problem on the third watch.  I was again told this issue is only covered under the limited 90-day warranty.

I’ve used each of the three watches as my everyday watch.  They are on my wrist 18 hours a day, 7 days per week.  Many times I wear the watch throughout the night as well.

I have no problem with this being an issue if Garmin would stand by their products.  I’m sure I am not the first person to experience this.   After three watches, all having the same issue, I’m confident it’s a design/cheap materials issue that Garmin is aware of but refusing to do right by their customers.

I love the functionality of Garmin products.  I’ve owned almost every Garmin GPS watch starting around 2000 with the old Forerunner 205 (I think that’s what it was).  I’ll fight with the company a little more, but if they decide to not stand by their product and replace this watch I’m done and will look to move over to Polar or Suunto.

I would love to hear if others have experienced this issue as well.



  1. Thanks for documenting your issues. I have the same issue with my FR935. I noticed it a *long* time ago, but, now 19 months into usage, it’s far beyond the 12-month warranty period. Garmin Support is now offering me a $99 refurbished model in exchange for my broken unit.

    I’m hoping the FR945 fixes the issue because I’d like to purchase one.

  2. I just had this happen to me today. I’ve had my 935 for about 6 months. It’s worked great and wear it literally all the time. The only time i take it off is to dry it after a swim or charge it overnight (1/week). Never dropped or smashed this watch. I’ve used it in multiple Tris, never had an issue until today.

    I did a trainer ride this morning before I went to work. I took my watch off placed it on my counter and showered I noticed what looked like a scratch on the backside of the watch, but the HR was reporting accurately- so I just ignored it. I was driving home from work and I took my watch off to charge it in my car. that’s when I noticed the scratch had gotten MUCH bigger. and the there were multiple scratches. Each scratch was exactly over the rectangles of the optical heart rate monitor. I put the watch back on after my drive home and my Heart Rate read 208-220 (this is more than 3x my resting HR- even with traffic).

    Don’t know what to do here. I’ve never dropped this watch, I’ve never so much as mistreated it in any way now the OHRM is not working which is going to throw off my HR data and my sleep data.

  3. Happening to me as well. My first Forerunner 935 started cracking 2018 summer, had just bought it in January 2018. I got a replacement unit in September 2018.

    Just yesterday I noticed that the 2nd watch has the same cracks appearing. It’s just sad.. I like the watch and features, but this is quite clearly some kind of design flaw. I wonder if the new models are the same, and if other brands Suunto or Polar has similar problem?

  4. I have the same problem with my Forerunner 235. I am using it since April 2018. It is absolutely great device, but breakage of the optical HR sensor is a big problem. I have solved it by buying of the belt HR monitor, so I wear it during my sport activities. But the disappointing from the broken optical sensor is here as well as loss of the waterproof function… By the way, the same problem I faced at my previous Garmin Vívosmart Optic. The optical sensor broke shortly after one year using. I will try to complain at Garmin my Forerunner 235, but I don’t hope in success 🙁
    The link shows the picture of my broken sensor.

  5. Hi, I have had this before and now happening again on my 3rd 935. Funny thing is that the support replied this time that it won’t affect heart rate measuring, while from my previous experience it clearly did. How is it with you, heart rate measuring still working ok?

    I was told that it is some kind of reaction to chemicals.

    • I began to alter my heart rate readings once the tracking got real bad. If you look at the 735xt in the picture, it was so bad that the whole top layer of the plastic was missing. There was a huge divot. The second layer then became white-ish and the HR readings were all over the place. It was unusable.

      As for the chemicals. That’s originally what I was told too. My most recent 945 starting developing cracks within 10 days. I used ZERO chemicals on my skin while wearing it in the first 10 days. For that watch, it had nothing to do with chemicals.

  6. Thank you so much for this post. I recently noticed the cracking on my own watch and was pretty upset especially because I knew I hadn’t hit it on anything. I found your link to your blog on some other forum and contacted Garmin support. They immediately said it needed to be sent in and it has so far been a pretty easy, no argument process! Will come back and update.

  7. I already left a comment in this forum about my cracked HR sensor at my Forerunner 235. It was after a very short time of using, in the meantime cracking continued and after about 18 months of using the damage was really bad. All the surface was chipped, some parts left the base material and, to be honest, I was surprised that the sensor still worked somehow. I have decided to repair it, so I can share my experience.

    Here is the link to the picture :
    The first picture shows the damage before I started the repair. I scratched-out all the chips which were not fixed well, I used a sharp hard pin for it. The base resin was still hard, so the second picture shows the situation after this chips removal. Next I mixed the epoxy, the type is clear from the picture. I filled the HR surface by the epoxy – not too much, just the amount giving the smooth surface. After 24 hours it was hard. Now I know that using of a bit “slower” epoxy would be better because this fast hardening one created little bubbles during mixing and bubbles couldn’t get easily out. “Slower” epoxy would give to bubbles better chance to escape.

    The result is very good, the HR works normally now and I am happy with the result.

    !! WARNING !!
    – If anyone will try this method for repair, it will be done on his/her own risk. This repair is not approved by Garmin. I don’t accept any responsibility for possible failing.
    – Test the epoxy before using. It must be clear after hardening, some epoxy are clear before mixing, but during hardening they become “milky”. Do the practical test, don’t rely on the statements of the epoxy manufacturer!
    – I didn’t test the if it is waterproof, but the epoxy should be waterproof.


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