I have a new house and had a 6 litre raise toilet eljer I believe is the brand installed. It does not flush well and appears to not allow the 6 litres to past before the flapper covers the drain. I checked the flapper and all looks good. Is there an issue with this manufacturer and should I have the toilet change out for another or is there a fix?
The flapper is raised by a chain/rubber strap and if it does not raise the flapper completely, it will close before the needed amount of water is down into the bowl. The chain should be "just" long enough to allow the flapper to seal, but no excess. Check to see if you have a lot of slack in whatever raises the flapper when you hit the flush handle.
If you have never made a mistake, you haven't done much.