gas cock 
Mechanism cutting off the gas supply when the water reaches the desired temperature.
pressure-relief valve 
Device for lowering the pressure inside the tank by releasing excess hot water.
overflow pipe 
Pipe through which water escapes when maximum pressure is exceeded.
control box 
Box containing the set of controls that measure temperature and operate the burner.
hot-water outlet 
Outlet pipe for hot water flowing into the hot-water circuit.