it has been making grinding noises for about 3 weeks now and steering is really heavy now l only checked the levels today and there is not a drop of fluid left

possibly a bit too late now but fill it quickly an see how it goes....you may have damaged the pump.

l have no idea what sort of damage this would do, but I'd say get some more fluid in soon!

id take it to a garage
just to check its ok, but more importantly to find & fix the leak

the steering is a 'slightly' key component. do not risk ur life (and other road users / pedestrains)

you may be OK on a Xara Picasso, but l had a probelm with a Xantia which turne out to be a £2000 bill as the whole steering/hydraulic system needed replacing bbut l do not think Xara is use the flyign carpet suspension of the Xantia so if it does need repalcing it should be significantly cheaper

you must have a leak. it wont do any damage to your car. but you surly must have known. what was happening. l will correct my self you have a very bad leak. you have fractured pipe. so get it sorted. good luck.

If the pump is starved of fluid for long then it does damage it. Try filling it up and see how you get on.

the pump could form a ''dry spot'' from going without fluid for a period of time. You may feel a grab turning the wheel left to right, thats the dry spot.

Top off ur fluid & u may want to add alittle ''lucas oil'' steering fluid.
l use it in everyone of our cars/trucks,you can feel the difference.

You can pick it up at any local automotive part store (autozone)

Lucas oil products
http://lucasoil.com/products/display_products.sd?iid=28&catid=2&loc=show

The power steering system does not lose fluid unless there is a leak. It is a sealed for life system. Apart from having the fluid changed on major service intervals it remains untouched.
The common fault for fluid loss is the power steering rack or pump leaking.
Suggest getting ur local garage (not the main dealer unless under warranty) to steam clean the relevant areas, top up the fluid & turn the steering from lock to lock several times & check for fresh fluid leaks.
This will isolate the problem & give a basis for repair costs.
Power steering pumps & steering racks can be overhauled or supplied on an exchange basis at a lot less cost than a main dealer part.

yes the pump needs oil for lubrication
the noise you heard was the pump sucking air

No, but please put power steering fluid in soonest. The fluid that they will supply you with is automatic gearbox fluid. It is the correct fluid.
Take your Citroen to someone competent to find out where the leak is in your steering box system.
Good luck