Well, not hearth related, but the hearth stuff is getting sort of slow this time of year, so.... My hot water flow is getting pretty slow. I have a oil furnace with a coil, and pretty hard water. (Yes I have a softener) I suspect the coil is getting pretty gummed up with mineral deposits. It's a Burnham circa 1987. Anyone know if the coil can be replaced or cleaned? The cleaning guy says it's running very clean and efficient, and I'd only gain 2-3% efficiency with a new one, so not worth replacing unless absolutely necessary.