how can I tell my Wrist HR monitor is working?

On one of the stock Fenix watch faces, I enabled HR as a data field but the value is always zero.
HR Widget shows something (albeit not always correct) but it does give me some inclination that its trying to measure something.
I see the HR sensors (green lights) flashing all the time
Yet, HR is always "0" on the watch face

The HR Widget history chart shows nothing for the last 7 days, even though I wear my watch every day

Is there something wrong with my watch's HR sensor?