This indicates the steam generator has gone into overheat protection mode. In the first instance, power the unit down and leave it for an hour to cool down and then inspect. Remember to ensure you power the unit off during inspection, never undertake this whilst there is power to the unit. If there is no evidence that the unit has sustained any damage and all pipework appears to be in order, power up the unit and run the generator keeping an eye on how it's operating. Periodically they can overheat if used for excessively long periods than that of what is recommended, so be mindful of this if it continually happens. We recommend 20 minutes at a time. 

If all the above fail to fix the issue, then it's likely the steam generator is faulty and will need replacing. If your product is under warranty, please submit a support ticket along with your warranty number to obtain a replacement. If outside warranty, please visit our spares section where you can locate a replacement.