I have a thing for idioms and one such idiom I regularly use is 'to set the heather on fire'. It fits well whenever referring to doing something sensational. Now, is there any alternative to this? Any other idiom or word which comes close to meaning the same?
I've never heard the phrase "set the heather on fire" before either. (Though as we speak, a nature preserve that borders my property is being set on first as some sort of environmental measure. They promised not to burn down my house in the process.)
If you mean "sensational" in the sense of "causing widespread interest and excitement", like might be caused by a radical new invention or a political movement, then "set the world on fire" is a closely-comparable phrase. Another would be "turn the world upside down", though I think that's getting antiquated. Or "upsetting the apple cart".
If you mean "sensational" in the sense of "acting wild", like a wild party, then "paint the town red" is a common American idiom. Also "running amok".
It's a pretty antiquated and uncommon turn of phrase - popularised if not actually coined in Walter Scott's 1818 novel Rob Roy. But (UK) Chambers Dictionary still includes the definition to set the heather on fire - to create a disturbance or a sensation.
To set the heather on fire is to generate great energy or excitement, and fire is the quickest way to do it in other expressions as well. The excited or energized people could themselves be set on fire: The proposal has set New York's chattering classes on fire; or The blogosphere is afire with the news about Breitbart. They can also be fired up, pumped up, all abuzz, or any other word or expression for having one's passion aroused.
If you want to emphasize the effect rather than the affected, you could say the causative agent is causing a stir (mildly) or hitting a nerve (jarringly). It may be making waves, ruffling feathers (causing mild discomfort), or rocking the boat (disruptively drawing attention).
I've never heard the idiom setting the heather on fire, and if I did I would probably take it to mean 'clearing the ground for something better', since I do know that landowners and forest wardens sometimes deliberately burn patches of old heather to encourage new shoots, buds and other wildlife-friendly growth.
But if OP wants 'doing something sensational', you could try on a roll, nailing it (for solving a specific problem), or firing on all cylinders.