pressure drop/increase baxi 105 e?

any help please. Always had a pressure drop on this boiler. keep topping up . thinking of using a sealer . Are they any good. added prob though. I noticed when checking pressure other day whilst Ch was on that the pressure went from 1.5 to over 2 and rising. Steadied when i turned heating off. Could the system be draining itself via pressure releif valve if pressure kept rising to ver 3 bar. And why would it rise