HRM Pro plus cadence reads 0 while running

Are all the other Running Dynamics including Ground Contact Time Balance recording OK with the HRM connected?

I specifically reference GC Balance as the other RD items can come from watch now so if HRM gets disconnected its not so easy to know apart form GC balance.

Maybe also try unpair and re-pair the HRM completely.

No, I can’t see any of the other information you reference.

It alerts me on the watch when I select run that HRM is connected.

perhaps not getting good skin contact, although I had it fairly snug.

That is strange...I'd try re-pair the HRM completely.

Also there is a hack to reset the HRM see the link attached 

forums.garmin.com/.../garmin-hrm-dual-not-working

Extract below

Please follow the steps below to perform a Reverse Polarity on your Sensor / HRM – this will reset the module and allow connection with your head unit;

• Take the battery out, and flip it over and insert it back into the  HRM to reverse the polarity
• Hold it in there for 5 - 10 seconds
• This will reset the HRM strap
• Then remove the old battery and install the new battery properly.
• Ensure the module is fixed to the strap correctly. (only applicable to HRM’s with removable module)
• If using a HRM, wet the electrodes on the strap & position it on your body securely as per the user manual instructs.
• Perform 5-10 start jumps to get your heart rate up & commence the pairing process.

You may be required to follow the pairing steps for each sensor after battery replacement as per user manual instruction.

Thanks I’ll try again tomorrow and maybe try the hard reset.

seems odd as it’s a brand new unit straight from the box.

Thanks for the help mate

Yes bit strange indeed. Good luck!