If you’re running Zwift on an iPad, like I always do, too, then you can only be connecting via BT as Apple devices lack the hardware to capture ANT+ signals.
On the pairing screen, you see the BT logo in the HR pairing window and also in the main pairing screen upper left, both circled in red:
I’ve tried to get a 0 bpm reading on my paired HRM (Wahoo TICKR), but can only manage it momentarily when connecting it to another app (Wahoo). From what I understand – and I’m as far from an expert as you’d like to meet – BT connection behaviour and capabilities vary widely between devices. It could be that your HRM is already actively paired to another connection and needs to be ‘forgotten’ on that one, or at least that connection needs to be broken by force-closing the active app or the device on which it is operating, in order for your heart rate to be readable by Zwift on your iPad.
I’ve read the user manual for your model, but it doesn’t go into any detail about multiple pairing. If it is broadcasting simultaneously via ANT+ to what the manufacturer refers to as the ‘master device’ (your bike computer?), perhaps that is contributing to this problem.
I’m also wearing an Apple Watch, but have never paired it to that iPad, so don’t know if somehow it could be interfering.
If it were me, I would try isolating the problem by:
- switching off (force closing) any other app and device (including phone, Apple Watch and bike computer) that could be communicating with your HRM,
- force closing the Zwift app on your iPad,
- powering off your indoor trainer,
- powering on your indoor trainer, and
- restarting Zwift on your iPad and going through the pairing screen procedure.
(This is all assuming that your HRM is operating correctly and that you have a good skin connection with the chest strap pads, etc., which is probable if you’re getting good readings using other devices.)
Wishing you well with this.