Radiators aren't heating up uniformly. Does it need a clean?

So, I think there are two potential problems: 1. The radiators are hotter at the top than the bottom. Difference varies, but the largest is about 15 degrees after 4 hours of the heating being on. What should the difference normally be? Here are some thermal images of the 5 radiators. The living room one (the largest radiator) seems to be the most problematic: 2. The boiler seems to do short cycles whilst the heating is on. It's set at 66 but it drops and goes up randomly. The room stat is set at 25 degrees and it only ever gets up to 14 degrees. Some other things that might help: *Boiler radiator heat set to 66. I've set it up to 80 to see if it makes a difference to the radiators heating evenly but it didn't. Just got hotter at the top. *The boiler is Duo Tec *The room stat control is in the coldest part of the flat where there are no radiators. During the images and video it was set to 25 degrees. *We've balanced the radiators. And in the images you'll see the long thin radiator is colder at the top, so we bled that one today. *Might be unrelated but both showers give either scalding hot water or really cold at the slightest change in temp on the shower temp dial. *There are two floors to the flat, the smaller radiator with curtains above it, is that loft room radiator. The boiler is on the first floor. The loft room is on the 2nd floor. It's a Victorian house conversion flat. *The very first radiator closest to the boiler has had the lockshield valve only opened a little bit and the temp is set low. It helped the last radiator in the loft to heat up much more quickly once we did that. That's why it doesn't look hot in the pics. Hope that helps with diagnosing the problem(s)!