Changed thermostat over heating and the heater inside is not working. Relays for the fans new and working now what

Try reverse flushing the cooling system, including the heater core, replacing the radiator (due to phosphate scale), and refilling with a 50/50 mixture of Dex-Cool and distilled water. This link may help:

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

It was very helpful thank you.

Or do I need to replace the radiator.

If you used just regular antifreeze you can have your radiator professionally flushed. You will need to replace the radiator if it leaks or the inside is extremely rusty.

2000 Montana I did not use Dex Cool when I witerized. Now is over heating. Can I have the system flush or do I have to change the radiator.

Try reverse flushing the cooling system, including the heater core, replacing the radiator (due to phosphate scale), and refilling with a 50/50 mixture of Dex-Cool and distilled water. This link may help:

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

God must have sent you to help me. Thank you. I will be praying for you.