Ensure that the evaporator is positioned correctly. Normally it takes about 40 seconds before you are able to see water vapor. The fireplace will then give a sound signal when it is ready. However, if the fireplace shuts down immediately after the sound signal then the water reservoir might be overfilled. Dry the tank with a tissue while making sure that you keep some air space in the tank and place it back. Dry with a tissue the water dish.
If this does not solve your problem, continue with the problem viewfinder.
Can the fireplace draw in enough air?
If the fireplace is not provided in combination with a Ruby Fires surround, check if the fireplace functions outsite the installation situation, the fireplace needs to draw in sufficient air.
Is the evaporator of the fireplace cleaned and decalcified?