Need advice on how to adjust a leaky tap

[ZeroTools]

I've recently had a 3-way kitchen tap fitted (hot, cold and filtered). It's been in a week and I've noticed it's weeping slightly from around the edge of the hot/cold tap head. I've taken the tap head apart, hoping to find a loose nut or washer that needed replacing, but I can't see how to adjust or access the part that's leaking. I've attached some pictures, the arrow indicates where it seems to be leaking from (around the blue plastic ring). Has anyone worked on a tap like this before and can anyone advise on how I remove/adjust this to stop the leak? I dont want to start pulling bits apart in case I damage it.

 

[just pumps]

That is the cartridge which has 0-rings around the outside, being so new can`t you take it back?

 

[ZeroTools]

Taking it back would require un-installation, which I was looking to avoid. I've actually managed to figure it out myself, there's a double ended threaded retaining ring that holds the cartridge in place. It's not obvious how to remove it - I ended up using a pair of long-nosed pliers up against the little metal tabs to allow me to undo it and inspect the cartridge. I'm hoping its just the case that it wasnt done up tight enough to press the sealing rings on the cartridge up against the corresponding holes in the tap body, so I've tightened it up to see if that works. I'll leave this post here in case anyone else has a similar issue.