Ideal Standard Toilet Cistern Overflowing

All concealed toilet cisterns work on the same mechanism most people call it in wall toilet or hidaway cistern be it gebritt ideal standard armitage shanks grohe etc etc.
Ideal standard toilet cistern overflowing. I m not sure how relevant these are. An overflowing toilet is a problem everyone will likely deal with at some point. I ve recently noticed that the water level in the cistern is at the top of the overflow and i ve noticed that there is a very slow trickle of. Any help on how to solve this problem would be greatly received.
Http www fixed1t co uk fixed1t ebay supporter htm if your toilet continues to dribble constan. The replacement cistern flush valve washer is available here. When the toilet is flushed the water keeps filling in the cistern and doesn t stop eventually running into the pan constantly. The toilet is a modern press button type flush.
Bear with me as it s my first time repairing a toilet. I have an ideal standard push button toilet which is presenting a problem. Toilet cistern overflowing we had a new toilet fitted two years ago and fitter told us that the water pressure was low so he removed a couple of washers within the flush system inside the cistern.