Friends have a gas central heating boiler installed in a cupboard adjacent to an outside wall. The flue and air inlet are of the balanced-flue type. The boiler is fixed to the inside face of the outside wall. As the room is being re-modelled, they have decided to brick up the cupboard on the inside. This leaves the situation that the only access to the boiler is from the outside, where there is a small access door. This door is about 60cm high by 45cm wide, the bottom being about 20cm from ground level. Since being put in, this door has been penetrated by two drainage pipes, and so cannot be opened. Our friends have been advised by their builder that he can cut a smaller access door, above the level of the drainage pipes. However, this will entail crawling on hands and knees from the outside, through this "cat flap" of a door, and access will still be impeded by water and gas pipes on the inside, which run around the boiler. I am very concerned that the proposed arrangement will be either unsafe, or unworkable, or both. Can anyone please advise?