What's that black grit in 15-year-old dishwasher?

Q: My dishwasher is a 15-year-old Whirlpool in apparently fine condition, except that it leaves black grit all over the dishes. It seems to be worse on the top rack with the glassware. I don't know whether it is worse up there because of the actual location or some other factor I haven't considered.

I have disassembled the two spray arms, removed and cleaned the filters and every other part I can get at, and I keep them all religiously cleaned out. I have tried using less detergent, more detergent, different detergent, a combination of borax and washing soda (which, incidentally, works great on aluminum cookware that would otherwise get that powdery tarnish on it with regular detergent), and yesterday ran a cycle using straight vinegar and clean glasses to flush out any deposits. It's still as bad as ever and has gotten worse over time.

There is no obvious corrosion anywhere. Where is this coming from, and why? I used to assume that minerals were precipitating out of the water, but now I don't know. The grit is black, not that rusty color that you get in faucet screens and showerheads. There is no apparent rust present in the grit. This dishwasher doesn't have an airlock, but the drain hose is looped up and down the way it's supposed to be. I'd hate to buy a new one and find the same problem.

A: This is a new one on me. A rubber fitting disintegrating? Readers, can you help?

Q: The salesman tells me heat pumps are great; according to him, they work better than a conventional electric furnace and air conditioner, and they run so much more efficiently that, in a few years, they save enough on electricity costs to pay for themselves. But I can't help noticing that nobody seems to have one, and if they're so great, why doesn't everybody have one? I've tried to research this on the Web, but haven't been able to find any objective information.

A: Gas and oil furnaces are cheaper to buy, cheaper to run and cheaper to maintain than an air-to-air heat pump. That pretty obviously explains their popularity. But gas and oil furnaces lack air conditioning, unless it is added as an extra-cost option. A stand-alone electric resistance forced-air furnace is cheap to buy (consisting basically of electric coils, a blower and some sheet metal) but gnaws ferociously at the pocketbook every month. But add a heat pump, and the heating bill goes down noticeably since it extracts heat from the air. In areas where gas is not available, propane (bottled gas) and heat pumps compete.

Pay for themselves? Yeah, eventually they will, compared to a straight electric resistance furnace. It might be longer than you think, but it will pay for itself, and leave you in air-conditioned comfort meanwhile.

I have a heat pump at my house and am happy with it, but then again I have no sewer or bus service, no gas in the street, no cell coverage, no high-speed Internet provider and no Thai restaurant within 20 miles. The latter is really hard to come to grips with; the rest I can live with.

Darrell Hay answers readers' questions. Call 206-464-8514 to record your question,