Hi avs,
That’s certainly unfortunate … and frustrating … but warranties only cover “defects” which is determined by the warranty exclusion and they don’t cover “virtual impressions” that comes from foam softening and the loss of comfort and support that can go with it. You can read more about warranties in post #174 here.
According to their warranty here … the warranty exclusion is 1.5" but there is also a “?” in the brackets which mention smooth top mattresses and I believe the exclusion for the bio-gel mattresses are .75". Do you know how deep the measured impression was?
There is really not much you can do except perhaps through the goodwill of a retailer that goes to bat for you and argues your case with the manufacturer and hopefully convinces them to make an exception. You could also of course tell them you plan to write reviews about their mattresses that don’t reflect well on them and try to “force” them to respond but in most cases this would have little effect if they are only complying with the terms of their warranty and could harden their position even more. Gaining their goodwill is usually more effective than threats. Ultimately they are “in the right” if they are only complying with the listed terms of their warranty.
Which version of the bio-gel did you buy … and do you know the specifics of the layering?
It may help to turn your mattress (if you haven’t already) to even out the wear (90 degrees if it’s an Eastern King and 180 degrees for any other sizes) and there are also some suggestions in post #4 here that may rule out some of the other causes that can lead to sagging and has some suggestions that may be helpful as well.
The first place I would start though (if you haven’t already) is by talking to the retailer where you purchased the mattress.
Phoenix