Heart Rate Issues
1. No Heart Rate signal at all
All SRM's sold by WiredBike use a Polar CODED strap, so if you have an older un-coded one, you need to upgrade. You will either get erratic heart rate signals, or none at all.
That being said, I usually don't start getting a signal 'til I sweat a little. No problem in July, but takes some time in January. Moisten the strap to get immediate signals
2. Erratic signals
Wildly high or low is caused by interference. Coded straps eliminate this problem.
"Off" signals, meaning somewhat high or low could be picked up from another rider. That also is solved by a coded strap.