Cambrian, the directions I followed in Chris Draper's book said walk up the lane about 150 yards from the Chapel and on the left, opposite those farm conversions go through the metal gate and keep to the right hand hedge until you reach another gate and look at the white house and stone barn across the stream.
I've enclosed another photo of the whole complex and the waterwheel is attached to the building on the left.
Is this the one you are talking about?