Customer has a 20+ year old tankless water heater that is not working as of two days ago. Pulled the cover off and cleaned out the burner chamber and checked all the components and insured that the unit is igniting. Called Takagi and they had a hard time finding info on the unit and told me the motherboard and the burner are giving an error code but the age of the unit makes it hard to get parts and expensive. Provided the customer with an estimate to install a new unit mounted on the side of the home.