NABIS small basin mixer problem

[mallard63]

One of these was fitted 2 years ago and worked fine until last week. Now the hot water side has reduced to a tiny trickle.
The copper pipe gets hot after 5 minutes so the water still continues to arrive,albeit very slowly. Flexi pipes run from the copper pipes to the tap unit itself.
I have taken the head off the tap to reveal the plastic cylindrical body of the mixer and have taken this out . I then turned the hot water supply on again and the water rose quite slowly up inside the body of the tap. Would that be normal and it is the tap itself that changes the force of water into a more substantial flow of hot water?
Or should the water have risen quite quickly?
I cant determine if the tap has failed or the pipework, yet the pipes havent been moved since installation and all was working fine up till now. Cold is still fine.
Any ideas anyone? Nabis have a 5 year guarantee apparently

 

[TicklyT]

Maybe the flexi tail has reached the end of it's useful life, the rubber liner blistered and closed up the bore......

.... or maybe there's just a lump of crud wedged in the relatively small bore of the flexi pipe.

 

[Terry lambert]

Couldnt have put that better

 

[mallard63]

TicklyT and terrydoh

Thanks for suggestions. I will give that a go. Didnt realise they had such a short life span!