Hi
There is no known issue with the heart rate sensor under watchOS 4.1.
The following steps may help:
Check your settings:
- On your iPhone, in the Watch app, go to: My Watch (tab) > Privacy - turn on Heart Rate and Fitness Tracking.
- On your iPhone, in the Watch app, go to: My Watch > Workout > turn off Workout Power Saving Mode, if it is currently enabled.
- On your iPhone, go to: Settings > Privacy > Motion & Fitness - check that both Fitness Tracking and Health are enabled.
Check that you have set up the Activity app:
If you are not yet doing so, use these settings:
- On your iPhone, in the Watch app, go to: My Watch (tab) > Passcode.
- Turn on each of Wrist Detection, Passcode and Unlock with iPhone.
- After putting it on your wrist, your Apple Watch will then unlock after whatever you do first: either unlocking your watch manually (by entering the passcode) or unlocking your iPhone.
- When worn sufficiently snugly, it will then remain unlocked (including when the screen is asleep) until you remove it from your wrist.
- When you remove your Apple Watch, it will lock automatically.
Close certain apps and restart both your iPhone and your Apple Watch:
- Close the Watch app, Activity app and Health app (if open) on your iPhone:
- Double-click the Home button, then swipe up on each app preview to close the apps.
- Turn both devices off together, then restart your iPhone first:
If the issue persists, then - given that you have already tried unpairing and re-pairing your Apple Watch - I suggest that you contact Apple Support (remote diagnostics and/or mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider for assistance: