steaming intermittently?

Tefal steam generator gu8120
My iron was steaming intermittently so I opened the tank stopper to flush it out and a small rubber thing with four prongs on the top, fell out. I looked like some sort of long filter ( finger shaped ) and was brown in colour. The iron is still only steaming for a few minutes and then stops. I would be grateful for any advice to save me spending out on a new one.