Forerunner 255 Series - Recent Threads

My Forerunner 255 is failing to record my sleep.

1345609 — Mon, 07 Sep 2026 16:27:05 GMT

My 255 suddenly started having issues recording my sleep score. All my settings are correct and haven’t changed, I have the watch tight enough on my wrist so that there’s no chance of it losing contact, it’s charged and I have no activity active or pause (like running, walking, etc). It’s recording all of my other data continuously throughout the night (heart rate, body battery, HRV, breathing rate, etc) just no sleep score. I’ve been sleeping soundly and have my sleep window on my watch set the same way it’s always been (11pm-9am). It’s worked perfectly fine for the past year then suddenly does this even though no changes have been made. I double checked all my settings and they’re correct. I also looked for updates and everything is up to date.

Battery drain 27.09

shefski — Sat, 24 Jan 2026 10:50:11 GMT

Hi, after recently updating to 27.09 on my forerunner 255, the battery life decreased drammatically (from 15 days to 1.5 days). Also, the sleep tracking no longer works and I feel like the watch has gotten slightly laggier. I have already restarted and reset my device a few times with no results.

Is this something others are experiencing as well? What's the procedure to fix this?

Thank you!

RE: Battery drain 27.09

3145842 — Mon, 07 Sep 2026 12:47:27 GMT

I like Garmin but they really seem to struggle with coding and testing of firmware updates. Best suggestion I have is to do a full reset of the watch, unpair from Bluetooth, uninstall/reinstall Garmin connect, then reconnect it to your phone. It's a complete pain but oftentimes will fix the issue. I agree though, if my watch finally breaks my plan is to move to Coros.

RE: Update 29.05

kegnatz — Mon, 07 Sep 2026 12:43:47 GMT

lights are working... sw ver bundle 29.05 [DFU e0c0de]....

Update 29.05

6544718 — Wed, 02 Sep 2026 09:48:38 GMT

I noticed some bugs since the new update was installed.

Speed in activity was not always displayed.

Training status stopped working.

Sleep status stopped working.

I am the only one?

RE: Update 29.05

Bit — Mon, 07 Sep 2026 09:24:54 GMT

Do the OHR sensor lights work? Are any of the versions listed under System -> About 0.00 or have an * after the version number?

Strava pulling through incomplete watch name from Garmin

jamiebee — Mon, 07 Sep 2026 08:57:00 GMT

Up until mid August, Strava showed my watch name as Garmin Forerunner 255 Music. For some unknown reason, since then it is showing as Garmin Forerunner 255 on all activities. I’ve tried removing the watch and adding it again on both Strava and Garmin. I’ve also tried signing out / back in again on both.

I’ve shown some screenshots from my Garmin Connect app showing on my Home page, the watch shows the shortened name but when I go to More > Garmin Devices it shows the correct name including Music at the end.

I’ve no idea why it would suddenly change for no reason. Anyone else had a similar issue and offer a solution ? It seems to be pulling through the name from where I click on the watch icon on the Home page.

RE: Battery drain 27.09

njgarde — Sun, 06 Sep 2026 11:26:50 GMT

Had this kind of software malware occur with my Fitbit so moved to Garmin. Seems Garmin can't be trusted to provide a quality product anymore so time to move to a new provider. Got an update last week and today battery drained from 100% to 5% in 22 hrs when it lasted 10 days when I first bought it. Very disappointed. Seems Chinese products are cheaper and more reliable

RE: R255S OWS distance bug – distance systematically lost after direction reversals (FIT/KML evidence)

kegnatz — Sun, 06 Sep 2026 11:05:33 GMT

Thanks... appreciate... this kind of swimming — repeating the same open-water distance back and forth — is actually the very reason I bought a Garmin watch, so I really care about getting it to work properly...

and to be honest I used ChatGPT to help me analyze and structure all the tests I performed into a clear and pragmatic bug report, rather than just reporting that “the distance seems wrong.” Hopefully the data will be useful to the developers and, above all, that they will consider it worth fixing.

R255S OWS distance bug – distance systematically lost after direction reversals (FIT/KML evidence)

kegnatz — Thu, 27 Aug 2026 12:31:24 GMT

I think I have found a reproducible Open Water Swim distance-processing issue on the Forerunner 255S.

This appears related to the previously reported “Forerunner 255 wrong open water readings” issue, but after several controlled tests I found a very specific and reproducible pattern:

the first straight leg can be measured correctly, but after reversing direction the OWS-calculated distance becomes systematically shorter than the distance represented by the GPS coordinates recorded by the watch itself.

Device: Forerunner 255S
Software: 28.05
GNSS: All Systems + Multi-Band
Recording: Every Second in the main tests (Smart Recording was also tested earlier)

Clearest test: 25 out-and-back legs, LAP at every turn

At a second location I swam 25 repeated approximately 60–65 m legs, pressing LAP at every reversal.

The first leg was essentially correct:

Lap 1: Garmin 63 m / GPS-coordinate geometry ~64.7 m

Immediately after the first reversal:

Lap 2: 49 m
Lap 3: 54 m
Lap 4: 55 m
Lap 5: 51 m
Lap 6: 56 m

...and the same pattern continues through the activity, with most subsequent laps around 44–56 m.

The key observation is:

START → first leg = correct
180° reversal + LAP → next leg = too short
another reversal + LAP → next leg = too short again
and the error repeats

Manual LAP therefore does not appear to reset whatever is happening in the OWS distance calculation.

Garmin Connect screenshot showing all 25 original lap distances:
https://github.com/kegnatz/garmin-fr255s-ows-bug/blob/main/Screenshot%202026-08-27%20at%2013.48.29.png

Complete FIT/KML evidence ZIP:
https://github.com/kegnatz/garmin-fr255s-ows-bug/raw/refs/heads/main/garmin_fr255s_ows_FORUM_FINAL.zip

Evidence repository:
https://github.com/kegnatz/garmin-fr255s-ows-bug

The GPS track itself is substantially longer

This does not appear to be explained simply by poor GPS reception.

When I calculate the geometric path length from the GPS coordinates recorded by the watch in the FIT/KML, the 25-leg activity is approximately 1595 m.

In other words, the watch has GPS positions representing substantially more movement than the OWS distance calculation credits.

This suggests that at least part of the missing distance occurs after the GPS positions have already been recorded, in the OWS distance-processing/filtering stage.

Test with only ONE reversal

To test this further, I did a much longer swim with only one major direction reversal, approximately halfway through, without pressing LAP at the turn.

Garmin KML GPS geometry: ~1509 m
Garmin reported OWS distance: ~1480 m

The first ~750 m leg appears to be measured normally. After the single reversal the activity ends approximately 29–30 m shorter than the geometry of Garmin's own GPS track.

Control test: one straight leg

I also recorded a simple single-leg swim with no reversal:

GPS-track geometry: ~158 m
Garmin displayed distance: ~160 m

So the same FR255S can measure a simple OWS leg essentially correctly.

Earlier tests show the same pattern

In previous repeated-leg tests I obtained approximately:

1491–1493 m Garmin GPS track → 1355 m reported OWS distance

and

~1515 m Garmin GPS track → ~1380 m reported OWS distance

Switching from Smart Recording to Every Second did not solve the problem.

I also tried wide, continuous rounded/figure-eight turns instead of stopping and making sharp 180° turns. Garmin simplified those curves in the recorded GPS track, but the calculated OWS distance was still materially shorter than the geometry of Garmin's own recorded coordinates.

My working hypothesis

My suspicion is that after a substantial direction reversal the FR255S OWS filter temporarily interprets legitimate movement in the new direction as GPS noise/drift and does not add all of that movement to distance.

After some time it appears to accept the new direction again.

That would explain why:

no previous reversal → first leg is correct

while

after reversal → the beginning of the next leg loses distance

and repeated reversals allow those deficits to accumulate.

Garmin engineering should be able to verify this directly by comparing FIT Record position_lat / position_long with accumulated distance immediately before and after each reversal.

Manual LAP clearly does not prevent the behaviour.

I would also be interested to know whether REST resets this internal state while LAP does not. I have not used a REST test as evidence here. Even if REST works, however, LAP followed by swimming in the opposite direction is a perfectly legitimate OWS use case and should not systematically lose distance.

Separate pre-start GPS issue

I have also seen another potentially related behaviour.

Before one swim I opened OWS and waited stationary for more than two minutes for GPS lock. I then entered the water, moved to the actual starting point, raised the watch above water and waited until GPS was green again, and only then pressed START.

Nevertheless, the exported activity used the earlier pre-start GPS-lock position as its starting point.

Files and methodology

Any manually drawn Google Earth route I used while investigating this was only approximate and is not being treated as ground truth.

The main evidence is the comparison between Garmin's own recorded GPS coordinates and Garmin's own calculated OWS distance.

I have also submitted this to Garmin Support.

Could anyone with a FR255/255S reproduce this?

A particularly useful test would be:

swim repeated equal-length out-and-back legs → press LAP at every 180° turn → compare Lap 1 with the subsequent laps.

I would also be very interested in the same test on other Garmin models to see whether this is specific to the FR255 OWS algorithm.[View:/cfs-file/__key/communityserver-discussions-components-files/649/garmin_5F00_fr255s_5F00_ows_5F00_FORUM_5F00_FINAL.zip:320:240]

RE: R255S OWS distance bug – distance systematically lost after direction reversals (FIT/KML evidence)

ovekvam — Sun, 06 Sep 2026 10:54:31 GMT

Nice work. It is very helpful for developers when users report bugs in such a comprehensive way.

RE: R255S OWS distance bug – distance systematically lost after direction reversals (FIT/KML evidence)

kegnatz — Sun, 06 Sep 2026 10:09:36 GMT

UPDATE – additional testing

I did a few more controlled tests after the original post.

The issue is not limited to sharp 180° turns. I also tried making much wider, gradual turns instead of reversing direction sharply, but this did not eliminate the distance loss. I also tested different turn angles. Examples of long sections:

GPS track: 404.1 m → Garmin OWS: 389.5 m (−14.6 m)
GPS track: 161.3 m → Garmin OWS: 147.0 m (−14.3 m)

The most interesting test was:

~850 m → STOP → 180° turn → RESUME → ~850 m

First leg: Garmin 851.5 m vs GPS ~850 m
Return leg: Garmin 848.9 m vs GPS ~852 m

So STOP/RESUME almost completely eliminated the usual distance loss after the 180° turn, whereas simply pressing LAP at turns did not.

This makes me suspect that STOP/RESUME resets some internal state/filter used by the OWS distance algorithm.

Obviously this is not a practical workaround — nobody wants to STOP/RESUME at every turn — but I think it is a useful diagnostic clue for Garmin engineering.

I have already sent the original detailed report and FIT/KML evidence to Garmin Support and requested escalation to the OWS/firmware engineering team. I’m currently waiting for their response. Once I receive it, I’ll send them these additional test results as well, particularly the STOP/RESUME finding.

RE: Update 29.05

kegnatz — Sun, 06 Sep 2026 09:39:59 GMT

well.... my standard usage is all health sensors off, background light after sunset 90%, many notifs/connection vibrations and approx 45 min/day MultiBand GPS + HR and it uses 16%/day, but I'd say just as it was before... and it seems kind of normal for a 3 years old 255s....

wrong training detection

8102785 — Fri, 04 Sep 2026 13:06:07 GMT

for the past 10 days, my Forerunner 255 has started detecting my bodybuilding sessions (three times a week) as low aerobic instead of anaerobic. As a result, my training status changed from unproductive to unbalanced. These activities are exactly the same as before, when they were recorded as anaerobic. I have already tried wearing a chest heart rate monitor and I have already installed all the latest software updates.

RE: Update 29.05

3145842 — Thu, 03 Sep 2026 12:58:05 GMT

After having fixed battery drain issue with the last firmware update, it’s back again. Normally battery would drain about 9% per day, now it’s over 20%. Going to try all the normal suggestions, but it’s very frustrating that every time an update rolls out the watch doesn't work properly.

RE: Does anyone please have the 255 music 28.05 FW file?

1860424 — Thu, 03 Sep 2026 11:48:49 GMT

Sorry mate, can't find 28.05 in this thread...

Does anyone please have the 255 music 28.05 FW file?

1860424 — Thu, 03 Sep 2026 11:02:31 GMT

Wanted to have a backup before I upgrade to 29.05 [emoticon:c4563cd7d5574777a71c318021cbbcc8]

RE: Does anyone please have the 255 music 28.05 FW file?

ronand — Thu, 03 Sep 2026 11:45:54 GMT

https://forums.garmin.com/sports-fitness/running-multisport/f/forerunner-255-series/433225/garmin-can-you-please-upload-firmware-26-08

RE: Anyone got the 27.09 file?

1860424 — Thu, 03 Sep 2026 11:00:15 GMT

Maybe you know the link to 28.05 as well, mate?

Anyone got the 27.09 file?

7694242 — Fri, 19 Jun 2026 06:02:02 GMT

The recent update really messed things up on my watch, I‘d like to downgrade to 27.09 again. Does anyone have the gupdate.gsp file for the non-music version left on their computer?

I accidentally recorded a multi-sport as all swim. Is there a way to fix it?

DrewKime — Sun, 16 Aug 2026 14:54:21 GMT

I ran a triathlon and had multi-sport configured to long-press the lap button for transitions. During the race I forgot and just short-pressed, creating new laps but not changing activities. Is there any way to convert this to the correct activities?

I also recorded the ride on my Edge 530, so I've got all the cycling data. For the run I probably won't get cadence, but HR and pace should be there based on the GPS.

RE: I accidentally recorded a multi-sport as all swim. Is there a way to fix it?

trux — Tue, 01 Sep 2026 20:26:15 GMT

[quote userid="305542" url="~/sports-fitness/running-multisport/f/forerunner-255-series/442042/i-accidentally-recorded-a-multi-sport-as-all-swim-is-there-a-way-to-fix-it/2057165"]You'd think this would be discoverable in the official documentation.[/quote]

And indeed, it is: Garmin Connect: Top Multisport Editing Tool FAQs | Garmin Support (see the Q "Can I Divide An Activity Leg?"). It took me 2s to find it with the simple query site:support.garmin.com "divide leg" - Google Search

RE: I accidentally recorded a multi-sport as all swim. Is there a way to fix it?

instezz — Tue, 01 Sep 2026 17:43:07 GMT

This happens to me basically at every race :D

So during last year and a half I worked on a set of scripts that would allow me to manipulate FIT (and other) files, because I was really frustrated by the lack of proper tools around.

I realized the amount of frustration from other athletes (not just in this forum) about the lack of an easy and simple “move the freaking transition” drag and drop tool… and I decided that maybe this could be useful to others.

So I built https://thesplit.fit. It’s free, it works in your browser, it’s designed to be simple, it doesn’t store your data, and it spits out a nice fit file for you to reimport.

Bonus: if you happened to record your bike leg on your bike computer you can drop that in and it will be substituted.

I am looking for people that can test it out and report bugs or ideas for improvement if anyone here has the same issue.

Try it out ;)
stezz

Ps. I tried the Garmin "divide leg" feature but that is exactly what it does: it divides a leg, it does not move the T1 start or end time. It cannot substitute a bike computer file for what was on the watch... I even tried to "restore orginal file" and after a few hours the activity page was still showing blank :/

RE: I accidentally recorded a multi-sport as all swim. Is there a way to fix it?

DrewKime — Thu, 27 Aug 2026 00:51:39 GMT

Thank you! You'd think this would be discoverable in the official documentation.

Forerunner 255 Series - 29.05 - 100%

Garmin-Kevin — Wed, 26 Aug 2026 17:50:50 GMT

Software Version 29.05 is now available for Forerunner 255 Series. You may manually download this software update by following the path below:

Menu > System > Software Update > Check For Updates

Change Log

Fix an issue with syncing strength personal records to Garmin Connect.
Fix an issue with configuring heart rate and power fields from Garmin Connect Mobile.
Various bug fixes and improvements.