Clocks are like faithful and reliable old friends. It can be a surprise when they stop working.
They might just need a bit of tlc, such as re-oiling. They might need more attention, such as a full service. The mechanism will be taken apart and placed in a specialist cleaning tank, each part is cleaned, however small or large.
Repairing a clock is not like repairing a car, the car goes to the garage and comes back the same day (hopefully!). Clocks need more time! After repair they need to be watched for about two weeks to make sure that they telling the time accurately. If they misbehave the fault has to be identified and put right, they will then need to go through the retesting process again.
After this work is done the clock is tested. We keep an eye on it to make sure that it is keeping time accurately. This is done in two stages, first it is checked whilst out of its case, then put back in and checked again. This is done over a two week period, if all is well the clock can go home.