Simple Plumbing Problem (I'm A Complete Newbie :( )

Hi every,
 
My toilet has just started trickling -- water is running slowly but continuously from the tank to the bowl. When I popped the lid off, I realized that the tank was so full that water very slowly spilling over into the overflow tube. 
 
I managed to stop the trickling by adjusting the "float cup" + its "box" (Fill valve?) very very far down its tracks. When the water fills, the float-cup & box are totally submerged -- the water level is about 2 inches above this floating mechanism! Even though the float is put so low, the eventual water level in the tank is only 1 inch below the outflow tube. 
 
People on the internet say that the tank should stop filling once float-cup floats up, but mine doesn't [as the float-cup floats up, then everything gets submerged by the rising water]. What might the problem be?
 
Thank you all kindly. 
 
Best wishes
Fiona

(I realise that this is an electrics problems forum, but if anyone has any DIY plumbing skills I would be very grateful!)

Yes the filling should stop as the float lifts up. it should not become submerged. A common problem with 'push button' toilets (which yours sounds like) is the diaphragm perforates. if you take a look at this youtube video, it shows how to get to the diaphragm to check it and replace if need be.

https://www.youtube.com/embed/X09OL1HD1HM?feature=oembed

probably needs a new valve, fairly simple to do if you have some pump pliers and silicone

ftsc said:

(I realise that this is an electrics problems forum, but if anyone has any DIY plumbing skills I would be very grateful!)

Click to expand...

This is an electrical forum, but there are a lot of interrelated areas of plumbing that have electrical connections, so we do have a pluming questions area. I have moved your thread.

Doc H. 

I'd say washer/diaphragm gone.

Do you live near a B&Q? They are a pain at times, but the fact you can go and compare your broken one with new ones in little bags is invaluable - because these things have many slight variations.

Dead easy. buy 2 and tape one to the underside of the cylinder lid.