Your Garmin Forerunner 935 has been your trusty workout companion for months, tracking every step, every heartbeat, every climb. Then one day, you finish a hilly run and check your stats, only to find your elevation data is completely flat or wildly inaccurate. Frustrating, right?
This issue is more common than you’d think, and the good part is that most cases can be fixed without sending your watch back to Garmin. Let’s walk through why this happens and exactly how you can get your elevation tracking back on track.
Understanding the Elevation Recording Problem
Your Forerunner 935 uses a barometric altimeter to measure elevation changes. Think of it as a tiny sensor that reads air pressure. As you climb higher, air pressure drops, and the watch calculates your elevation based on these changes. Pretty clever technology packed into something you wear on your wrist.
But here’s where things get tricky. That little sensor has a tiny hole on the side of your watch case. This hole needs to stay clear so air can flow in and out freely. When it gets blocked or the sensor gets confused by sudden pressure changes, your elevation data goes haywire or stops recording altogether.
You might notice your watch showing zero elevation gain after a mountain trail run. Or maybe it’s recording elevation, but the numbers make no sense. Sometimes it’ll show you climbing hundreds of feet while running on a perfectly flat path. These are all signs that your altimeter is acting up.
If left unfixed, you’ll lose valuable training data. Your VO2 max estimates become less accurate, your training load calculations get skewed, and you can’t properly track your progress on hilly routes. For serious runners and athletes, that’s a real problem.
Garmin Forerunner 935 Not Recording Elevation: Common Causes
Several factors can throw off your watch’s ability to track elevation properly. Let’s look at what’s usually behind this annoying issue so you can pinpoint what’s affecting your device.
1. Blocked Barometric Sensor Port
That tiny hole on your watch case is more important than it looks. Over time, dirt, sweat, sunscreen, and dead skin cells build up around it. Even soap residue from washing your hands can clog this opening.
Think about how much your watch goes through during workouts. You’re sweating, maybe running through dusty trails, applying sunscreen before outdoor activities. All that gunk slowly accumulates around the sensor port.
When the port gets blocked, air can’t reach the sensor properly. Your watch essentially becomes blind to pressure changes, which means it can’t calculate elevation. This is actually the most common culprit behind elevation tracking failures.
2. Outdated Software or Firmware
Garmin regularly releases updates that improve sensor accuracy and fix bugs. Running old software is like trying to use a map from five years ago in a rapidly changing city. Things just don’t work as smoothly as they should.
Each firmware update includes tweaks to how your watch processes altimeter data. Some updates fix specific bugs that cause elevation glitches. Others improve the algorithms that filter out false readings from sudden temperature changes or weather shifts.
3. Incorrect GPS or Sensor Settings
Your watch has several settings that affect how it records elevation data. If GPS is set to UltraTrac mode to save battery, elevation accuracy takes a hit. Same thing happens if you’ve accidentally disabled the altimeter or changed calibration settings.
Sometimes after a software update or factory reset, settings revert to defaults that aren’t optimal for elevation tracking. You might not even realize a critical setting got flipped until you notice wonky elevation data.
4. Poor GPS Signal During Activity
While the barometric altimeter does the heavy lifting for elevation, your watch also uses GPS data to cross-check and refine those readings. Running through dense forests, between tall buildings, or in narrow canyons limits GPS accuracy.
When GPS signal is weak or keeps dropping, your watch struggles to correlate barometric readings with your actual location. This creates confusion in the system. The watch might second-guess its altimeter readings or fail to record them properly.
Cloudy weather, heavy tree cover, and even the position of your wrist can affect GPS reception. If you’re running with your watch hand close to your body or covered by a jacket sleeve, signal quality drops noticeably.
5. Extreme Temperature or Weather Changes
Your altimeter measures air pressure, but temperature and weather also affect pressure readings. Moving from a heated car into freezing outdoor air creates a sudden pressure shift that can confuse the sensor.
Storm systems bring rapid pressure changes that have nothing to do with elevation. Your watch might interpret these as climbing or descending when you’re actually on level ground. Flying in airplanes or driving through mountain passes can also throw off calibration.
Garmin Forerunner 935 Not Recording Elevation: How to Fix
Getting your elevation tracking back doesn’t require any special tools or technical expertise. Most fixes take just a few minutes and can be done at home. Here’s what actually works.
1. Clean the Barometric Sensor Port
Start with the simplest fix first. Locate the small hole on the side of your watch case. It’s usually between the buttons or near the charging port.
Take a soft-bristled toothbrush and gently brush around the port opening. Don’t poke anything into the hole itself as that could damage the sensor. Just brush the surrounding area to remove visible debris. You can dampen the brush slightly with water, but make sure it’s not soaking wet.
For stubborn buildup, use a cotton swab lightly moistened with rubbing alcohol. Gently clean around the port area, then let it air dry completely before wearing the watch again. Do this cleaning every few weeks if you work out regularly or live in dusty conditions.
2. Calibrate the Altimeter Manually
Your watch needs an accurate reference point to measure elevation changes from. Open the altimeter widget by pressing the up button repeatedly until you see the elevation screen.
Hold the down button to open the options menu, then select “Calibrate Altimeter.” You’ll see two options: Auto and Manual. Choose Manual if you know your current elevation. You can find this by checking online elevation databases, topographic maps, or even asking a smartphone app.
Enter your known elevation carefully. Even being off by 50 feet can affect accuracy throughout your workout. After calibration, do a test activity on a route where you know the elevation profile. This confirms whether the calibration stuck.
3. Update Your Watch Software
Connect your Forerunner 935 to Wi-Fi or plug it into your computer with Garmin Express open. The software automatically checks for updates.
If an update is available, let it download and install completely. Don’t interrupt the process or disconnect your watch. Updates can take anywhere from five minutes to half an hour depending on file size and connection speed. Your watch might restart several times during installation.
After updating, go for a short test run on a familiar route with known elevation changes. This helps you verify that the update improved tracking accuracy. Many users report immediate improvements after updating to the latest firmware.
4. Reset GPS and Sensor Settings
Sometimes your settings get corrupted or misconfigured. Press and hold the menu button, then go to Settings. Navigate to System, then select Reset.
Choose “Reset Default Settings” rather than deleting all user data. This preserves your activity history and personal information while resetting system configurations to factory defaults. You’ll need to reconnect to Wi-Fi and re-enter some preferences afterward.
Pay special attention to GPS settings after the reset. Make sure GPS mode is set to “GPS + GLONASS” or “GPS + Galileo” for best accuracy. Avoid UltraTrac mode unless battery life is absolutely critical, as it significantly reduces tracking precision.
5. Perform a Soft Reset
A soft reset clears temporary glitches without erasing your data. Hold down the Light button for 15 seconds. Your watch screen will go blank, then the Garmin logo will appear as it restarts.
This simple reboot often fixes sensor communication issues. After the restart, open the altimeter widget and check if it’s reading properly before starting an activity.
6. Test in Different GPS Environments
Take your watch outdoors to an open area with clear sky visibility. Wait for the GPS to fully lock before starting an activity. You’ll know it’s ready when the GPS icon stops flashing.
Run or walk a route with noticeable elevation changes. Hills, bridges, or multi-story parking garages work great for testing. Compare your recorded elevation against what you know the actual change should be. If accuracy improves in open areas but fails under tree cover, you know GPS interference is part of the problem.
7. Contact Garmin Support or Service Center
If you’ve tried everything and elevation still won’t record properly, your watch might have a hardware issue. The barometric sensor itself could be damaged or failing.
Garmin support can run diagnostics and determine if your watch needs repair or replacement. If your device is still under warranty, they’ll handle repairs at no cost. Even out of warranty, repair costs are usually reasonable compared to buying a new watch.
Wrapping Up
Elevation tracking issues on your Garmin Forerunner 935 usually come down to a dirty sensor port, outdated software, or calibration problems. Starting with a thorough cleaning and manual calibration solves most cases right away. Regular maintenance keeps your watch accurate over the long haul.
Your elevation data matters for training insights and progress tracking. Taking a few minutes to troubleshoot now saves you from missing out on valuable metrics during your workouts. Keep that sensor port clean, stay updated on firmware, and your watch will keep delivering reliable elevation stats for years to come.