Chain set Issues

That's an interesting one. I'd argue that a bike shop will at best have run a tension check on those bolts at service. I can't imagine they'd have stripped the rings for the service.

Therefore, why did the rings come loose? 

anyway, I'd argue this has nothing to do with Giant, potentially has something to do with the bikeshop, and something to do with the owner.

That last point however is the tricky one. If you are paying for someone to maintain your bike, then  thats what you expect them to do. As said above, 4 months is a long time not to have someone service a bike, so either the bikeshop needs to be demanding more of your reddies for more frequent maintenance,  or there is an expectation that the user will be doing basic maintenance at home.

Tricky. 

The fac t that the bikeshop ar egoing to Giant suggests they don't feel culpable. 

That wasn't properly serviced/installed. It sounds like the chainring bolts weren't installed with some threadlock compound which is just careless and they weren't sufficiently tightened as well. I'd expect Giant or the bike shop to make good on the damage as it's a result of incorrect installation.

I've had two 105 chainsets do this. Each time taking a chunk out the frame. Both manufacturers were willing to look at compensation (Cannondale, Ribble) but I didn't have much faith in them paying so used the £40-odd quid I'd have used shipping them off on a check from a mechanic and a bottle of appropriate nail polish (for the frames, not for Friday Night) 

with one id tried to rethread it so that was a warranty write off, the other I sent back to ribble and paid the cost difference between 105 and Ultegra (£27 at the time) and got that as a replacement 

they can and will shake loose I check them weekly now and use threadlock

Back in the day loose chainring bolts were a regular thing - I often lost one or two. Not had it happen in the last 20 years or so.

You really should be spotting stuff like this when you clean your bike - you do clean it don't you?

Never experienced loose chainset bolts in 25 years of riding except when I forgot to tighten them! What a numpty. So it should be a warranty claim

I wouldnt say 4 months is an unreasonable time for chainring bolts to loosen. Should be up to you to check your bike regularly in addition to bike shop services.

Hmm.  Not sure that's a warranty issue or a service issue.  Either or both of Giant or the bike shop might provide a degree of assistance as a goodwill gesture, but I'm not convinced you have much of a claim against either.  But I talk as a punter with no legal training / experience.

Chainring bolts are subject to some pretty significant forces, and combined with changes in temperature and moisture (winter to summer to winter) can come loose.  And once they start to get a little loose, they can get very loose very quickly.  I've just suffered this problem on both my most regularly used bikes, resulting in a bit of paint damage on one where the loose bolt(s) was scraping against the chainstay.

It was not all that obvious in normal riding that the bolts were loose - what gave it away was that when changing gear up or down at the front, the chain was sometimes not engaging as well/quickly/smoothly as I was expecting, or was falling off.

I'll be keeping more of an eye on this in the future.

Fingers crossed for you, different situation, but for reference I have a Giant moutain bike which has failed three times at the same point (weld of top tube & seat tube). Each time Giant have sent the shop a replacement frame (and rear shock) without a pause. They might not be the best bikes in the world, but their attitude to their customers seems pretty good to me.

It's a tough one Harry.  On one hand, as you say, the shop serviced it only four months ago and *should* have checked every fastener and Giant *should* have installed the bolts using threadlock.  On the other hand, a chainring bolt that loosens off sufficiently to fall out (and the others must have been loose as well for the chainring to touch the frame) is something that the rider ought to have noticed while riding/cleaning/lubing the bike, giving the shop the opportunity to remedy the problem before any damage occurred.

I would be very surprised if you get a new frame under warranty, but the shop may offer you some goodwill - perhaps contribution towards repair of the frame, or a free service - but I wouldn't expect much.