I have a Roca toilet installed in my downstairs toilet. For the last 6 months or so it has had a very poor flush, not enough to clear everthing out the pan. The flush is also quite noisy. The house is only 18 months old. I have tried a new dual flush mechanism to no avail and the drain has been checked and runs clear and free. Buckets of water poured into the pan drain with no problems. Even by removing the flush mechanism and pouring water straight into the cistern seems to take a while to drain from cistern to pan. I have tried to clear the holes under the rim but they seem clear enough. Any other ideas i have missed?