I have a 4 family home with an ancient oil boiler that's been services well and has new devices (gauges, safety equipment, etc.).
The external tankless coil hot water heater (with aquastat) doesn't seem to be doing the trick any longer.
That is, after a few minutes of running the hot water, the water turns cold. But, the cold doesn't seem to bring the boiler's water temperature down to trigger the aquastat to turn on the boiler.
I know there are more efficient ways, but I'd like to get this working without much change for the time being.
Is it possible that there's too much corrosion inside the external coil? Possible to use a chemical to clean it? Any other possible solution?
Thanks very much,