Zipper, I would certainly push the issue. Often warranted requires return to base as you did and it's still not working that is big time getting stuffed around.
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I would be seeking a full refund or new replacement .
Bugs me when business stuff people around and myself find it is cheaper for me and more satisfying for the customer to deal with it properly the first time.
Example I some a unit and after they installed I got a call it was not working properly, having established the had done the trouble shooting as best they could I arranged to do the 1 hour drive to do the trouble shoot myself in case they missed some thing.
In doing that I considered that if in fact the unit was faulty it would be cheaper to remove it, bring back for repair than sent a techician up to do it on site but that would also mean having to getting the unit back.
My solution was to take a new replacement unit with me, I established the unit was faulty so replaced it there an then, Client is happy as and I can deal with my supplier re the faulty unit while minimising the cost to them.
It is difficult when clients are in regional areas but you did you bit, they failed
