Another thing to check is that the new pads are seated correctly. A common fail is where people don't get the boss on the back of the pad sat in the piston notch.
****, how big a fail is that? I've just done my rear pads and discs, confirmed to work as the rears get pretty toasty after a short non-enthusiastic drive. No heavy resistance in spinning the wheel when jacked up either.
Also when trying to refit the pad carrier, I stupidly started it up and pumped the brakes with thinking it would help align the 17 mm holes but the piston seal started dribbling brake fluid. Probably lost about 10 ml. I eventually got it all back together, pumped it on a fresh patch of ground and no more fluid was ejected. No dribbling after a short drive also, have I ****** up?

I know, I should have just paid somebody for it...