Crisis over, mystery solved! I'd been overdosing. Backed off the dose, upped the grind (ie. finer), a cooling flush, a second or two of manual pre-infusion. Shot was a P.B.- delighted. Thick, rich, balanced, crema has good colour now, not pale any more. Using Proud Mary's Eagle Vision blend. Sorry for panicking, I got the machine fairly cheap & was worrying it was a lemon.
Next problem to solve is the milk. Steam tip has 4 holes, I can't seem to get a good rolling swirl happening to make a good microfoam. Much more steam than previous machine, so things happen faster. Perhaps a different tip, fewer holes, so more unidirectional?