Polar F6 Question

[Zula]

I have a polar F6.

 

 

 

My question is when I stop exercising, say to change a tube, and I move away from the unit (which is on my handlebar), it loses my hearbeat. It continues to time me until I stop it, just without the hearbeat value.

 

 

 

So how do I get it to re-pick up me heart rate once it loses it for a period of time. Ive tried pausing the workout and then pushing continue but it does'nt work.

 

 

 

Any ideas?