Isolate the water supply because the toilet cistern has to be removed to do the job. When the water is isolated, make sure you flush the toilet and use old cloths to wipe out any water that is left inside the cistern. Undo the water supply from underneath the tank. Now, undo the bolts that hold the toilet cistern to the pan. Take the chain from the handle. Brockley Plumbers carry all the right tools for this. Lay the cistern down onto an old towel. Remove the large rubber spud washer and its nut at the bottom of the flush valve using a wrench. Remove the old flush valve and place the new flush valve inside the valve hole and check the top of the overflow pipe. This should be at least 1″ under the cistern high level marking and the hole where the handle is fitted. Put the flush valve below the handle lever arm, fixing it to the cistern from beneath with the spud
nut. Tighten up the nut just a bit more than hand tight using a spud wrench or channel type pliers. It is possible to crack the cistern when tightening any fittings. Fit the new spud washer over the spud nut, small side down. Place the cistern down with its face upwards and put the correct washers onto the tank bolts and feed into the holes from inside the cistern. Fit the brass washers and hex nuts on the bolts from underneath and tighten them a little more than hand tight. Now place the cistern over the pan and sit it down so that the washer sits over the water inlet in the pan and the cistern bolts fit through the holes in the pan flange. Connect the cistern and bowl. Alternatively you could hire a Brockley Plumber to do the job. Connect the water supply at the fill valve inlet. Refit the chain clip on the handle. Connect the refill tube back to the top of the overflow pipe.
Switch the water supply on at the stop valve and test the flush.