Sync problems with your Garmin 840 are annoying. Really annoying. Your workout data sits trapped on your wrist while your phone pretends the watch doesn’t exist. I’ve fixed hundreds of these issues over the years, and here’s what you need to know: most sync failures have simple causes that you can fix yourself in under 10 minutes.
This guide covers the actual reasons your watch stops syncing and gives you real fixes that work. No tech jargon. No vague suggestions. Just clear steps based on what actually fixes these problems most often. You’ll learn what breaks the connection between your devices and how to get them talking again so you can see your stats where they belong.
Why Your Garmin 840 Stops Syncing
Your watch and phone need to work together for syncing to happen. When your Garmin 840 won’t sync, something broke that connection. Maybe Bluetooth isn’t working right. Maybe your app lost its permissions. Maybe a bad file is stuck in the queue. But the data is still there on your watch, waiting.
Here’s how syncing works when everything is fine. Your watch uses Bluetooth to connect to your phone. It bundles up all your workout info and sends it over. The Garmin Connect app on your phone grabs that data and pushes it up to Garmin’s servers. After that, you can see everything on any device where you’re logged in. Simple process. But if any part of this chain breaks, nothing moves.
Skipping syncs creates real problems. Your Garmin only stores so many activities before it starts writing over old ones. Let too many pile up, and you’ll lose data permanently. That 50-mile ride you crushed last Tuesday? Gone. Plus, your training metrics get stale. Body Battery, training readiness, recovery time—all these features need fresh data to tell you anything useful.
Your watch might also give up trying after too many failed syncs. It stops attempting automatic uploads. Even after you fix whatever caused the problem, you’ll need to manually force a sync to get things moving again. The watch isn’t damaged. It just stopped trying because nothing was working.
Garmin 840 Not Syncing: Common Causes
Most sync issues come from the same few problems. Once you know what usually goes wrong, spotting the issue becomes easier.
1. Bluetooth Connection Issues
Bluetooth being “on” doesn’t guarantee it’s actually working. Your phone’s Bluetooth can get stuck in a strange state where it looks active but isn’t really doing anything. Your phone might have connected to your car speakers or wireless headphones and completely forgot about your watch. Happens all the time.
Distance plays a big part too. Bluetooth has a range of about 30 feet, but that’s in perfect conditions. Put your phone in another room or stuff it deep in a gym bag, and the signal weakens fast. Walls block it. Other devices interfere with it. Even keeping your phone in your back pocket while wearing your watch can create connection issues.
2. Outdated Software on Either Device
Old software causes sync problems because devices stop understanding each other. If your watch is running outdated firmware, it might speak a language your updated phone app no longer recognizes. Works the other way too. An old app version can’t handle data from a newly updated watch.
Software updates come out regularly. Miss one, and you risk compatibility headaches. Your watch tries sending data using new methods that your old app has never heard of. This happens a lot after big phone system updates, which change how apps talk to Bluetooth accessories.
Sometimes updates download but don’t actually install right. Your device gets stuck in a weird halfway state. It thinks it updated, but the software is broken or incomplete. You won’t see an error message about this, which makes it hard to catch.
3. App Permission Problems
Your phone decides what each app can do. Garmin Connect needs permission for Bluetooth, background activity, and location access. Turn off any of these—either by accident or through a system update—and the app stops working properly. It can’t do its job without the right access.
Background running matters more than people think. Many phones restrict apps from running in the background to save battery. If your phone does this to Garmin Connect, the app gets killed halfway through syncing. Looks like a failed sync, but your phone just shut down the process before it finished.
4. Corrupted Activity Files
One bad file can stop everything. Maybe you ended a recording in an odd way. Maybe your battery died at exactly the wrong moment during a save. Whatever happened, that corrupted file now sits in your sync queue. Every time your watch tries to sync, it hits this broken file and can’t continue. Everything else is perfectly fine, but this one problem blocks the entire line.
Finding the bad file takes work. It could be from days ago, just sitting there waiting to upload. Your newer activities stack up behind it, all stuck because of this one troublemaker at the front of the queue.
5. Network Connectivity Problems
Bluetooth might connect your watch to your phone perfectly, but if your phone has no internet, the data has nowhere to go. Common problem in areas with weak cell signals or spotty WiFi. The sync starts, then hangs, then fails because Garmin’s servers never receive anything.
Data settings cause issues too. Some people set their Garmin app to only upload on WiFi. If you’re on cellular data right now, nothing syncs. The app follows your rules exactly, but it feels broken because you forgot what you set up months ago.
Garmin 840 Not Syncing: How to Fix
Time to fix this thing. These solutions work for most sync problems and don’t need any special skills or tools.
1. Restart Both Devices
Sounds basic, but restarting clears out all the temporary junk that builds up in your device’s memory. Hold the power button on your Garmin 840 until you see the power off option. Shut it down. Then turn off your phone completely. Wait 30 seconds. This isn’t busy work—the pause matters.
That 30-second wait gives your phone’s Bluetooth chip time to fully reset. Turn both devices back on and they’ll connect fresh, without carrying over any weirdness from before. Open Garmin Connect and check if syncing starts automatically.
No automatic sync? Swipe down on the app’s main screen to force one manually. You’ll see a spinning circle while data transfers. Be patient, especially if several activities are waiting to upload.
2. Forget and Re-Pair the Bluetooth Connection
Sometimes you need to completely wipe the connection and start over. Go to your phone’s Bluetooth settings. Find your Garmin 840 in the list of paired devices. Tap it, then choose “Forget This Device.” This erases all the saved connection info.
Now open Garmin Connect and remove the watch from there too. You’re starting with a clean slate. Hold your watch close to your phone and add it back through the Garmin Connect app. The app guides you through pairing, takes about a minute.
3. Check and Update Your Software
Open your phone’s app store. Search for Garmin Connect. Install any available updates. For your watch, open Garmin Connect, find device settings, and check for software updates. If one’s available, charge your watch to at least 50 percent first. Low battery during an update can cause bigger problems.
Updates take 10 to 20 minutes. Your watch restarts itself when done. Don’t mess with it during the update. Don’t try using it. Just let it finish. After both devices run current software, try syncing again.
Some updates need WiFi instead of using your phone’s connection. If you have the WiFi version of the 840, connect to your home network and check for updates directly on the watch through system settings.
4. Reset App Permissions
Go to your phone’s settings. Find the apps section. Look up Garmin Connect. Check what permissions it has. Make sure it can access Bluetooth, location, and storage. Turn on “Background App Refresh” or whatever your phone calls the setting that lets apps run when you’re not using them.
iPhone users might need to turn on “Precise Location” too. Android users should verify the app isn’t being battery optimized, which stops it from running properly in the background. After you change these settings, force close the app completely and open it fresh.
5. Delete Problematic Activities
Got a corrupted file causing problems? You need to remove it from your watch. Press and hold the menu button on your Garmin 840. Go to History. Look through your recent activities. See one that looks weird or incomplete? Select it and delete it.
Try syncing with Garmin Express on your computer instead of your phone. Computers sometimes handle broken files better than phone apps do. Connect your watch using the charging cable. Open Garmin Express. Let it sync. This might push the problem activity through or at least show you which file is causing trouble.
After removing bad files, try syncing to your phone again. If you deleted an activity you wanted to keep, check Garmin Connect on your computer. Sometimes bits of corrupted activities still reach the servers, and you can recover partial data.
6. Contact Garmin Support
Tried everything here and your watch still won’t sync? You’ve got a deeper problem that needs professional help. Contact Garmin support. They have tools that read your device’s internal logs and spot issues you can’t see from the outside.
Your watch might have actual hardware damage to its Bluetooth chip. Or maybe something’s wrong with your specific account on Garmin’s servers. Support walks you through advanced fixes or sets up a repair if your warranty still covers it. Don’t open the watch yourself. Don’t use random repair shops. Both kill your warranty instantly.
Wrap-Up
Most Garmin 840 sync problems come from stale connections or outdated software. A quick restart or fresh pairing usually fixes things in minutes. Work through these solutions one at a time instead of trying everything at once. That way you’ll know what actually worked.
Keep your software current. Check your app permissions occasionally. These two simple habits stop most sync issues before they start. Don’t let workout data pile up on your watch too long either. Sync regularly so you catch problems early, while your data is still safe and recoverable.