This is a really great question! You actually would not be able to cause a hurricane by putting hot water into the sea. It takes a LOT of heat to warm the ocean, and climate change is already doing that for us enough!
You are correct in thinking that hurricanes form over warmer waters, but to make hurricanes, you also need wind. As winds pass over the ocean, it causes the warm, moist ocean air to evaporate and rise up into the atmosphere, where it cools to form storm clouds. Eventually the winds will start rotating, and if the winds get strong enough (<74 mph), you get a hurricane.
So, in addition to warm water, you have to have very strong winds as well. NOAA has a great infographic for kids on how hurricanes form, and I've included it for you here:
I hope this has answered your question. Have a great day!