Yes the cartridges do have a float inside. The printer throws a bean of light lat reads the ink level. This is thwarted by a black bit of plastic on the refillable carts. However on mine they also have the chip. I presume this counts the amount of runs the cart has done? Still messing with it to get it working again. I have a feeling that the carts I bought were not the best and the company I bought them from give zero support and almost never answer their phone. Swapping the chips around a couple of times looks to have done the trick.
Still had no blockages and printed almost 200 a3 transfer sheets.