Open the cover, check whether the spare parts are old. Many parts can be bought from from shop. I did that on my own to stop the leak even though I am not a technician, If you call the plumber, they will charge high fee, kena cheated before, so I decided to fix it on my own.
usually it's the stopper that is not sitting snugly on the hole. it can be a chain in the way or the stopper well has worn out. check stopper first. if all are ok, check height of float ball when water is full. water may be leaking via the overflow as float ball may be set too high.
Usually water leaking Jon-stop is due to valve faulty.
Just take a photo of the valve system in the cistern. Go to a shop that sells toiletry stuff and buy a similar valve unit. Be sure to buy one of similar height as these valves comes in different sizes.
Turn off the tap supplying water into the cistern, Remove the cistern where it holds the water, change the clave, put back the cistern. Just a couple of plastic screws to remove and put back.
As simple as that. No brainier.
Not sure where you are, dyi cost is about one-fifth of what you pay if you get a plumber.
Just open the top cover. Look at it where doest it leak.
If you not sure what size, Just open it bring to hardware shop.
It will cost few $(valve) to max $20 if u change whole next set internal.
why need to spend a single dollar?
I called my town council hot line and they send a technician to fix it FOC.
remember you pay cc/sc charges? make your dollar work harder
if they refused, tell them like that why we vote for you?stupig