Looking at the heart rate when running, there is usually a dramatic increase after about 10minutes. Dont think it is an effect of my equipment.
I would argue that the first 10 minutes are likely erroneous readings - it is not really conceivable for your heart rate to shoot up by 40bpm for no increase in effort after 10 minutes. The steady increase in heart rate after this point is characteristic of cardiac drift - the increase in effort for maintained pace.
How do you measure your heart rate? Using a chest strap, a optical wrist sensor, or the contacts on a treadmill? It is not uncommon for problems to arise with poor contact if using a chest strap (that's why it needs to be relatively tight, and lubricated to ensure it reads properly), with a watch being too loose if it has an optical sensor (not to mention if you have hairy/tattooed arms).
If you have any queries about using HR, don't hesitate to ask, as I've been using it as a training tool for a few years now.