It always impresses me the number of machines that can be made to work again just by banging on them.
The gasman was at my house today looking into why the radiators on the top floor don’t heat. The first thing he did was take the plastic knobs off the valves and then proceed to pound on them with a wrench. He explained that the valves have wax in them which expands when heated. This pushes a pin into place to close them, but occasionally they get stuck in the closed position. Banging on them frees up this pin and allows the valve to open. Several minutes later, they were heating again!
Our washing machine also responds favourably to a good thrashing. It occasionally develops a error with the (electronic) front panel which stops the washing cycle and causes the machine to beep incessantly. A quick slam near the front panel and it picks up where it left off as if nothing had happened.
Some machines need to be explicitly designed to be resistant to shock and vibration—aviation comes to mind immediatly. But many ordinary machines seem to get “stuck” for lack of a more precise word. Corrosion, disuse, or foreign matter clogging up the works. A quick shock to the system is sometimes all it needs to get moving again. Maybe in the future, before calling the repairman, I’ll be less hesitant to take matters in my own hands and start by swinging something heavy.