Tankless water heater working poorly, called tech ...

Tankless water heater working poorly, called tech support, they ran me through some tests and told me I needed 2 parts. Called Rheem to inquire about these parts, they were of no help, and would only tell me to go to Home Depot, that they can't deal with customers directly, Home Depot was of no help either, this heater is 4 1/2 years old. Bought a replacement Rheem hot water tank, never opened it, returned it. I'll never buy another Rheem product.