New duel flush issue

[livewire99]

Hi I recently had a Duel flush toilet installed works great , but at random usually when left for some time a thin trickle starts running down the pan and after a length of time after trickle starts the toilet starts trying to fill and making a hiss Noise , Its never stops trying to fill (very minor input of water) until you flush then can go away and no trickle or fill until a few hours later.

Its not high enough to reach overflow and is random when it happens usually after toilet left alone for some time.
I have removed the flush valve which is a 90 deg anticlockwise turn and checked round silicon ring all seems ok replaced it tight still same issue.
the fill side of it seems to be ok its not overflowing via overflow pipe.

Its only been in a few weeks any ideas is it just a bad one and i need to replace?

 

[CountryFan]

Possibly not seated correctly on the donut washer or could be intermittent issue with flush valve or detritus in the cistern? Maybe call the installer back?

 

[livewire99]

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