sticking 1/4 turn mixer

[rusky]

My bathroom mixer is getting really stiff to turn after less than a year. It's an Ikea one http://www.ikea.com/gb/en/products/...tap-with-strainer-chrome-plated-art-60281375/

Since it's a pain to take it off, & drive 90 miles to return it, I would rather see if I can fix it but I can't work out how to get to the cartridge inside!

Any ideas?

 

[Newboy]

Either behind the h/c index or to the rear of the tap handle there may be a fastener concealed (usually hex head)

 

[Newboy]

Either behind the h/c index or to the rear of the tap handle there may be a fastener concealed (usually hex head)

 

[rusky]

I've tried to get the h/c index out but it's not budging.