clean coil or buy indirect water heater?
Currently have a Burnham furnace coil that heats our water. And we have hard water (tested at 93 mg/L - best if does not exceed 150 mg/L), no softener (our laundry and dishes always are clean). When we moved into our 1968 house seven years ago, had plenty of hot water. In the past two years, hot water has decreased significantly (2 minute hot then warm water during shower, followed by 5 minutes cold water, then hot to warm water again) - but pressure is great.
This summer, our oil company recommended we remove the furnace's mixing valve because deposits rendered it ineffective. It helped and allowed us to have warm showers. Now 6 months later, we're back to the 2 minutes warm/5 minutes cold water cycle. Our oil company recommends a 40 gallon Crown indirect water heater installed for $1,995. However, one of the reps instead suggested we get an "old time plumber" to flush the coil for a few hundred dollars. Our oil company doesn't perform this because the toxic cleaner is "too dangerous."
My question: if our water pressure is great, our laundry washes white and our dishes have no discoloration, are deposits really the problem in our coil? Or something else?
Appreciate your thoughts!