Hi am new to this forum.a signed up looking for advise.i have a worchesrer 28cdi combi and when a checked it yestersay i saw the presure was down as soon as went to top it up warer starting pouring boiler,after i removed the cover the leak is coming from the copper pipe inside it has a white collar type thing around the pipe,can anyone tell me what the white is and whats inside it and it be fixed cheers