I have a towel radiator that really needs bleeding however I'm concerned that my boiler is going to need repressurising after bleeding. Most tutorials I have seen have had 2 blue taps that you need to open in order to increase pressure, however mine has 4 black taps and a yellow tap. I can see that it also has a notice about a pressure relief valve? Sorry I'm a novice at these things but don't really want to have to call someone out. The boiler is a baxi duo tec 2 28 ga combi. Any help appreciated.