Hi my toilet is flushing only just,the cistern only seems to be half emptying the water. I know its not the diaphram as this was replaced 3 months ago. Anyone know the solution please.

Is you commode an old commode or one of the new 1.6 gallon per flush? I am not sure what you mean by (diaphragm) but I think you mean the flapper that sets the water flow from the tank into the bowl. The new commodes use a different flapper than the old ones. Even plumbers have a problem getting the commodes to flush the way they should because of all the different brands and the minute differences in the way they are made.

You may have installed LowFlush Flopper. Lots of floppers on market these days are for Low Flush toilets. These floppers close too quickly emptying only about 1/3 of toilet tank per flush.