Toilet button won’t rise and water trickles into bowl

[Monaco]

This happened few times in the past few months.
Toilet is at least 7 years old.
I push the dual flush button and toilet flushes as normal. But the button will stay down and will not rise.
Water is then trickling into the toilet constantly.
I try to push the button down further (it’s already far down anyway so doesn’t go down much further) and nothing happens, it won’t flush.

I’ve solved it so far by lifting the lid and using a kettle to pour cold water into the cistern. And this solves it temporarily.
But this problem is happening every week- anyone know why?
Thank you

 

[blup]

If the pan is continuously filling, but water level is below overflow mark, replace the flush valve

 

[dilalio]

Take it out and give it a good clean.
Or just replace.