What is wrong with my Miltoniopsis?

[Fuggs]

Hi all

I bought a Miltoniopsis last week, think its "waterfall" I bought it because the fragrance was beautiful. Now after a week, the flowers have drooped, and they are developing black shrivelled areas at the end of the lower petal.

Was watered yesterday by immersing in rain water and a little feed. The leaves look nice and green, no dead tips.

Its difficult for flowers where I am, and I live in an old cottage, windows are small bit light seems ok. The room is heated by a Aga stove 24/7.

Any ideas guys please. Dont want to lose it if I can help it.

Thanks Fuggs