Too high risk, and too costly, but mostly a huge risk. It may triggered an unwanted uncontrolled eruption. Which may destroy the local area, grind European flights to halt, cause global cooling, kill all life... etc.

Also that boiler you want to stick in, will need to be made of some exceptional heat resistant material. And probably be replaced very frequently. Not very easy and very expensive. :)

But Iceland do have a lot of geothermal steam based generators.