The four X and Y axles are locked in place by pulleys. It is possible that one or more of the pulleys will loosen over time, which can alter their position. If this is the case, there could be play on the X and/or Y axles which in turn will lead to issues with print quality.
It is recommended to check for play on the axles at least once every three months.
Start with the right Y axle. Place the print head in the back-left corner to keep it out of the way. Hold the frame of the Ultimaker 2+ with one hand and firmly grab the right Y axle with the other. Attempt to move the axle forwards and backwards; do not be afraid to apply too much force.
Repeat this for the other axles; move the X axles side to side and the Y axles forwards and backwards. Make sure to move the print head to the opposite side each time.
The axles should not move at all. If one of the axles does move, you can observe a ticking noise of the pulleys hitting the frame. In this situation, it is recommended to calibrate the print head.