Cistern valve leaking into the pan

[Tally101]

HI All
my cistern valve is sometimes leaking into the pan, its a https://www.screwfix.com/p/viva-button-handle-dual-flush-valve/6998h
I have cleaned out the cistern so as nothing is stuck under the valve , does this mean the valve needs replacing.
Thanks

 

[CBW]

Probably just the sealing washer wants cleaning or replacing. Try removing it and put it back on the opposite way to original.

 

[oldbuffer]

Two possibilities:
1. The flush valve has a faulty seal, in which case replace the seal as CBW suggests.
2. The inlet valve is faulty, and allowing the water level to climb to the height of the internal overflow. In which case replace the diaphragm washer in the inlet valve or replace the whole inlet valve. Either is a water off job.