Hi every one, first post on the forum! I was just checking the pressure of my central heating system as i had noticed the radiators were taking ages to heat up. It was down at around .25 bar. I opened the tap to increase the pressure to the correct level and bled the radiators just to make sure there was no air. All seems good now. I did notice a crusty green slightly damp bit of what looks like corrosion on a joint at the top of the boiler. See the photo. Is this likely to be where the water is leaking and causing the prsssure to drop? Also was wondering what the part would be called if i have to speak to plumber on the phone. Thanks for any advice!