Hi and welcome to Just answer.
Initially, E05 is priming issue you can try to enter a service menu.
Service Menu: immediately after you switch it on press the LR, UL, UR, LL buttons in that sequence. Then you find the pump test and run it manually. You should got the expected water heating message upon the next restart.
If still, it possibly have airlock in the pump and water intake system
Try to manually prime your machine, for instruction CLICK HERE it supports all gaggia and seaco models.
Sometimes you need to get rough on your machine in able to remove the clog air on water line. slamming the water tank into machine sometimes help. If still, unplug your machine, remove water and turn the machine upside down or shake your machine if possible.
Let me know if you still have questions.
Hope this information will be helpful.
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