Hi I have a baxi boiler behind fireplace in the cupboard beside fireplace there is a pipe that has a screw thread in it but no screw this is where it is dripping the cupboard is dry but can tell damp over time, salty deposits also I know nothing about boilers but don't want to be ripped of by engineer as last person to touch was engineer last year, can you tell me if pipe should be open and dripping or requires screw also name of pipe please pic attached thank you