[richards]

NS Thank you. I tried the same way. but It doesn't move. Will there be a problem if I pull it by forcefully? Or should I press the gray button with a bigger force than I thought?

I am not a mechanic however the heat passing through the hose often times creates a bond with what it is attached to. A lot of twisting and pulling might free it enough to slowly pull away.
i am from the days when you climbed in and hit it with a hammer. Not sure about doing that today.
good luck