Power Steering Check

Hi. Lost power steering today on my 200tdi Defender. Can anyone advise how I can check if it is the pump or the box? There is no pump noise when I rotate the steering wheel as there used to be, especially on full lock. When I undo the bleed nipple some fluid flows out but very little and slowly. There is no gush of pressure or fluid, just a slow stream.

I recently removed my 2.5td and fitted the 200tdi. I used the old box but the 200tdi pump that was on the engine. I was told this was OK. Could this have caused a failure!?

Hope someone can help…. Easter Monday job awaits!

is the pump still working?
the belt hasnt come off?

Belt is tight and is not slipping. No leaks from system, fluid level remains constant.

Does anyone know how to check the pressure or if the pump is working properly without all the special tools and pressure test gauges?