Show me / explain how you would check that the power assisted steering is working before starting a journey?
If the steering becomes heavy the system may not be working properly. Before starting a journey two checks can be made. With the wheel turned slightly, maintained while the engine is started, you notice a slight movement in the wheel as the system begins to operate. Alternatively turning the steering wheel just after moving off will give an instant indication the power steering is functioning ok. Make sure you have checked the car has its handbrake on and is in neutral.