The real issue here is the difference between "what's reasonable" and "what's legal".

It's true that it's far more inconvenient to go several weeks without your Sears water heater working than it is to go several weeks without your Sears lawn mower working, but Sears is in the same legal position in both cases. They don't have to put any greater priority on getting the water heater up and running any sooner than the lawn mower.

So, you can appeal to Sears, and a reasonable person would agree that you've been inconvenienced, but keep in mind that they're not obligated to do anything more or do anything differently than they would if it was your Sears lawn mower that was on the blink. The warranty reads the same in both cases.