Cistern fill problem

[solo]

Hi all.
Got one of those push button, bottom entry toilets. Apparently when it's flushed the refill is very slow unless a cold tap is turned on then it fills as normal. Anyone got any ideas? This is not something I've come across before. I'm suspecting a floating blockage but I'm not there and can't look at it. Any help appreciated.

P.S. Off the top of my head it's a Fluidmaster fill valve.

 

[solo]

Been on Fluidmaster website. Looks like a replacement is needed.

 

[Richardthe3rd]

If it's a equilibrium float valve it maybe worth stripping it down & checking if there's any sh.t in it.