How does this Aqua Hot thing work?

[kgchampagne]

The 02S uses standard automotive antifreeze, and it can do this because the coil is on the outside of the tank. Newer models have the fresh water coil inside the tank, which is more efficient but because EG is toxic they had to switch over to a non-toxic antifreeze (boiler fluid). Replacement overflow tanks are easy to come by. I would recommend you buy a replacement filter and nozzle from Roger Burke so you can service it yourself, and you will learn a lot about the system in the process.
I would still take a sample of your fluid and send it in for analysis. This will tell you what you have in there and if it has the proper PH, freeze protection and you will know what you can/can't add. Your switch is in fact mis labeled, which is no big deal now that you know, but I ordered a replacement rocker cover for mine at a cost of about 10 bucks when I couldn't find a replacement.

[ByeTheWay]

If you are a DIYer, Professional help is free at: Roger Berke: RV Hydronic Heater Repair - Home He makes his money selling parts, which I find very reasonable compared to others.

[Flyin4Fun]

Originally Posted by Topman

Our switch did not light up either so I replaced the small led bulb and it is okay now.
Iver.

Bingo! The internal bulbs in those switches burn out before the life of the actual switch contacts. (In my experience)