Help needed with Polti Inox 5000R vertical steam not working!?

I am having problems with my polti iron it appears to be working normal i.e. all lights come on and it heats as per normal however when I press the vertical steam button it just makes a pressure noise for about 3 seconds and there is a puff of steam then nothing!!

I have tried cleaning the tank just incase there was a blockage but although it has helped slightly there is still no steam and instead it just releases water and it is still making the same noise.

Please can anyone help as I am lost with out my iron :(