Functional problems with doors include damage to the door material (rotted wood, buckled metal, et cetera). Door hinges which are damaged or poorly secured make doors difficult to open and close and, if not corrected, will lead to damage of the door and the frame. Latching mechanisms which do not work properly impair security. If the door is not properly weather-stripped, unnecessary heat loss is experienced. Frames which are damaged or out of square result in heat loss and doors which may be hard to open and close. Door thresholds which are loose or damaged are unsafe and should be repaired or replaced as necessary.

Sliding glass doors often suffer hardware damage or the track becomes dirty and the doors will not operate easily. On older metal sash sliding doors, the damage to the building interior at floor level can be significant, as a result of condensation and ice build up. The absence of a thermal break in the metal frame leads to a very cold interior metal surface. The cold metal contacts warm moist air in the house. As the moist air is cooled, condensation develops as droplets on the metal frame. The water runs onto the floor, or forms ice temporarily and as it thaws, will melt and run onto the floor. This damages the door sill, floor boards, subfloor and, in severe cases, the joists and header below. Providing an additional sliding door on the exterior will minimize the problem, although this creates a door opening which requires a number of motions to open and close. The preferred solution is, of course, to replace the sliding door system. Typically on these older systems, the hardware is not in good shape in any case.

Damage to the frame is common on sliding doors. This is often caused by excessive force used in opening and closing the door, often necessitated by damaged or poorly adjusted hardware, or a dirty track. Where the guides or rollers have been mechanically damaged, the door will not ride freely.

Ideally, all doors should have at least a six inch step up from the outdoors to the door sill. This is often omitted on sliding doors leading onto a deck, for example. Where this step is not present, snow accumulation on the exterior can leak through the bottom of the door system readily. Where no six inch step-up is noted, good inspection practices and regular maintenance (including snow clearing) are often necessary to prevent serious water damage.

The loss of a seal between double glazed panes on a sliding door is common. This results in a clouding of the glass which may be permanent. Because of the large panes of glass usually involved, this is a relatively expensive problem. Replacement is not a high priority as only a very small loss in energy efficiency is suffered. Replacement is usually undertaken because of the unsightly appearance of the clouded glass. Some door sashes are arranged so that they can he dismantled. Others are manufactured in such a way that this cannot be done. Replacement is, of course, more expensive in the latter case.