Heater will not get warm when you cut it on

Reverse flush the cooling system, including the heater core. Corrosion or phosphate scale may be blocking passages. Refill with a 50/50 mixture of recommended antifreeze and distilled water. This link may give you a new perspective on cooling system maintenance:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-3.html#post235973