Sensor problems

Heart Graph requires use of an external sensor for measuring heart rate, for example:

  • Apple Watch
  • Bluetooth 4.0 sensors
  • ANT+ sensors when connected via the Wahoo Fitness Key, an external dongle

Given the number of possible combinations of model of iPhone, iPad and iPod, different versions of iOS and the many types of heart rate sensor available, sensor connection problems are remarkably rare. However, we understand that when they do occur they’re frustrating, so we’ve collected together our advice on how to solve them.

There’s no need to ‘pair’ your Bluetooth/ANT+ sensor explicitly with Heart Graph – the first time you start a new workout, the app will automatically connect to the first heart rate sensor it finds. For subsequent workouts, Heart Graph will only try to connect to this sensor (so, for example, if you train in a gym, the app won’t  be confused by other people’s sensors). If you change sensor, have multiple sensors, or find Heart Graph has connected to the “wrong” sensor, you can register up to 4 valid sensors in the Heart Graph settings.


Heart Graph is known to be compatible with the following Bluetooth sensors, although many other Bluetooth sensors can also work with the app:

  • Garmin HRM-Dual
  • Mi Band
  • Mio Alpha
  • Mio Alpha 2
  • Polar H7
  • Polar H10
  • Scosche Rhythm+
  • Wahoo Blue
  • Wahoo Tickr

Connection issues with these (and other) Bluetooth sensors should be resolved by following the step-by-step tips below.

The following sensors regularly cause people to be directed to this page; please see the linked posts for more information on how to proceed.

Apple WatchPlease ensure that Heart Graph is set to “Apple Watch” mode on your iPhone. Note that Heart Graph cannot connect to your Watch from an iPad.
FitbitUnfortunately Heart Graph is not compatible with Fitbit sensors.
Garmin HRM (not Dual)The Garmin HRM sensors use ANT+, which requires use of an external dongle.

Step-by-step tips

The tips below are for any Bluetooth 4.0 sensor connection, although some of the advice will also be applicable to ANT+ connections via the Wahoo Fitness Key.

  1. First of all, ensure the basics are right:
    • Your iPhone/iPad has Bluetooth 4.0 support. (Bluetooth 4.0 was first available in the iPhone 4s and the iPad 3; earlier models will not work with Bluetooth 4.0 heart rate sensors.)
    • Bluetooth turned on in the Apple Settings of your iPhone/iPad; if already enabled, try turning Bluetooth off and on again in the Apple Settings app (not the Control Centre).
    • Heart Graph is permitted to use Bluetooth in the Apple Privacy settings: Apple Settings app -> Privacy & Security -> Bluetooth.
    • Heart rate sensor battery OK.
    • Sensor not paired with another device
    • If you’re using a Mi Band sensor, see this post for how to start the heart rate recording.
    • The sensor must be snug-fitting on your body to maintain good contact as you move.
    • Most sensors detect electrical signals from the heart, and the contacts must be moist for this to work. Particularly in cold climates, you may not sweat enough to keep these moist until some minutes into your workout.
    • Try pairing your sensor explicitly in the Heart Graph settings: first delete any existing sensors that are listed, then tap “Search for sensors”.SearchForPairedSensors
    • Try the “Alternative sensor connection” functionality in Heart Graph (this feature is currently in beta development – please let us know whether it works for you).
    • Take a look at our Known Issues page to see if there is already a work-around for your particular sensor.
  2. Do other heart rate apps work on the same iPhone/iPad?
    • Heart Graph uses software provided by Wahoo Fitness to connect to your sensor – if the Wahoo Fitness app is working, it is very unusual for Heart Graph to have problems.
    • Some heart rate sensor manufacturers offer the ability to update the firmware on your sensor. You should follow any manufacturer instructions for this procedure very carefully.
    • It may help to turn your iPhone/iPad off and on again to clear out any Bluetooth cache problems.
  3. Can you see heart rate data in Apple’s Health app?
    • With iOS8 and later, you can now pair a bluetooth heart rate sensor with Apple’s Bluetooth settings, which on an iPhone will store all heart rate data in the Health app. You should be able to see your heart rate changing in real time when viewing the Heart Rate section of the Health app, as shown for iOS 8, 9 and 10 in the screenshot below (for iOS 11 and newer, you must tap “Show All Data” and drill down to the current date to see the live heart rate values being added to Health):HeartRate
    • If your sensor will not connect with Health, we recommend you contact your sensor manufacturer for support.
  4. Perform a hard reset of your sensor
    • If your sensor uses the traditional button cell battery, you can reset the sensor by briefly inserting the battery the wrong way around, before then putting it in properly again.
  5. Delete and reinstall Heart Graph
    • This drastic option will cause all data stored within Heart Graph to be deleted; however, if that data is in Health, you can re-import it afterwards.
  6. Access heart rate data in real time from Health rather than with a direct connection to the sensor:
    • If you’re still having problems with Heart Graph, but you can see heart rate data with Health (see above), Heart Graph will automatically try to receive data from Health rather than directly from the sensor. To configure access to data in Health, please take a look at our short tutorial video:Health-as-Sensor-(en)Please note that if you are using this option, you must keep Heart Graph as the foreground app on your phone, and keep the screen on during workouts.
  7. Let us know if you’re still having problems