My HR often seems to rise in the first half mile or so and I put this down to the aerobic system kicking in. I have had high heart rate readings before (once when climbing up onto Askham Fell 205 bpm) and i dont think it was due to interference or having just done the Bob. It may be the sensors but I tend to get no reading at all if the sensors arent moist.
Nevermind I seem to be OK so I wont worry too much although I would have freaked out a little had I seen 225 flashing at me though!!!
Thanks Gaz