"Marilyn & Bob" wrote in message
...
Before buying a whole new system just because the coil is failing, I would
suggest buying a separate water heater. Install the water heater in
series with the output of the tankless coil so that hot (or at least
tempered) water goes to the heater and thus requires much less energy to
bring the water in the heater to the necessary temperature.

Separate heater may be a good idea, but not in series with a clogged coil
that can restrict flow.

As for replacing the entire system, that depends on payback and present
efficiency. In the right conditions, the systems is free of cash outlay.
My interest free loan is $67 a month, but my savings in oil is bout $70.