Yeah I don't mind doing it, it's more remembering to do it
My original Navien unit kept failing on the water flow sensor, I think it was just a poor design. I have a newer model Navien now that's been fine. I wouldn't say the water here in East York is "soft" by any means either, my humidifier gets pretty gross in the winter. Even though this newer Navien says its lower emissions, it still can smell a bit rich outside if it's short cycled. Not sure if that's common or not...
Granted we replaced furnace and went tankless together, but our gas bill dropped drastically in doing so. Also nice having "unlimited" hot water. Don't think it's paid off though, especially having to replace it once already, though I guess I could have just kept buying new flow sensor yearly. The gained floor space was helpful though since the tank was right in the path into the storage space.
I've always had issues with the Navians. Rinnai will slow flow rate to maintaining temperature. Navians sacrifice temperature to maintain flow which is why they have flow rate sensor issues. You'll always have more issues with Naivians when the incoming water temp drops. They flat out don't work at Big White.