I didn't use my Gaggia Factory for about 2 months cause Ive been too busy with school and now I want to use it again. I thought I had emptied it but I apparently forgot to and left about 1/2-1/3 of a tank full of water in it by accident.

What should I do to clean it before I use it again so its good to go? Thanks!

I would treat it the same as a descaling with a couple liters of descaling solution / citric acid; it's available at brewing supply stores, health food stores, and some supermarkets labeled as "sour salt".

Dont stress.
Just empty it out, flush it a couple of times, refill with fresh water, turn on and run some water through the group to re-moisten your parched seals and you should be set. 2 months of non use should hopefully be not long enough to cause your seals to dry out. You will soon find out in your first proper pull.

Cold, stagnant water does not cause limescale, but tastes horrid and in a Factory/Pavoni, would taste like metal. As long as you empty it and give it a good flush you will be fine.

Of course there is never any harm in checking for limescale. Shine a torch into the boiler to see if you have any green scale build up when your boiler is empty. If you see anything then you should descale (plenty of resources on this site for this - citric acid, cleancaf are often mentioned).

If all ok, welcome back to your Gaggia Factory. She has missed you.

ziobeege_72 wrote:Shine a torch into the boiler

and by torch he means flashlight.

ziobeege_72 wrote:Cold, stagnant water does not cause limescale, but tastes horrid and in a Factory/Pavoni, would taste like metal.

To be clear, I suggested citric acid for its cleaning properties, not limescale removal. Another option is Urnex Cleancaf, a commercial boiler cleaning product, but it is essentially citric acid and a mild detergent.