Reflexs diesel heater : lid repair and cleanup?

[jorxster]

Howdy,

I've got a Refleks diesel heater which has come with my boat (1987 Feltz Skorpion III -- corten steel).

1. The lid has taken on a rusty texture, and I'm not sure what material it is, some sort of steel, cast iron? should I use a phosphoric acid rust-converter on it, or should I "season" it like cast iron -- bake with oil on it to protect the metal (though that could be greasy to handle)
See attached photo.

Also wondering, there used to be a copper coil in the heater before I bought it, now there's simply holes, which I've plugged with aluminum foil for now.
I've been wanting to run a system through the boat again, wonder if buying a copper coil from the company is the only option (assuming copper deteriorated from the salty sea air, I'd possibly prefer steel or something more durable). Any tips for recreating the water heating system to spread heat to the cabins fore and aft.

Cheers,
Jordan

[GordMay]

Refleks Manuals
➥ https://refleksheaters.eu/customer-service/manuals/
➥ https://refleks.se/wp-content/upload...g-engelska.pdf