Renault Clio heavy steering

If you have checked tyres ,which is a good idea in this cold weather.

Also raise the vehicle at the front off the floor. Leave ignition lock off and move steering from side to side. You will feel the stiff spot, then disconnect one side ball joint, if tough spot gone then you know it is that ball joint at fault.
Do a similar excersise with both Track rod ends if problem still there ,disconnecting one at a time.

After all checks there it is either the rack itself or the coupling to the steering column, in this weather all the salt etc is the most commen fault.

Obviously before all those checks please check if vehicle fitted with power steering that you have fluid in the resevoir.

Have you checked the power steering pump belt??? If steering is really heavy as you say, then that would be the first place I would look...