Why does my Tefal 2941 only give intermittent steam?

I own a Tefal 2941 steam generator. Lately, the machine heats up as normal, provides steam but then runs out of steam. I fiddle with the switch and eventually it will go through a re-heat process although this does not take long. It then steams again for about a minute and then stops. My husband has replaced the thermostat but to no avail. Can you help?