Living With Our Rapido 963f Le Randonneur Motor Home.

Thursday, 15 November 2012

Electrolytic Corrosion

In June last year I reported on the outcome of an unexpected early failure of the water jacket in our Alde gas central heating boiler, see: Boiler repair update. The result was we ended up scrapping the old boiler, replacing it with a new Webasto Thermo Top C diesel unit, which included remedial carpentry where the old boiler had been removed from.

Having just received the December edition of Waterways World magazine, which includes an informative article on all aspects of boat heating, I read that the Alde boiler utilises aluminium in its construction, which dictates that no copper can be used in the heating system due the the effects of electrolytic corrosion, see: for well described images of all types of this phenomenon.

A retrospective check on my heating system reveals all the pipework to be of the flexible type - so no problem there. However, the calorifier, which was installed by the boat builder in September 2004, along with the heating boiler, is constructed of copper. When using the Alde boiler, a stainless steel calorifier should be used, according to the WW article, so that the problem of corrosion doesn't occur. Here is a link to the Alde website Q and A section, where it states clearly that copper should not form part of the plumbing circuit. Alde website.

This is another one of those quirky little things that even the most astute boat surveyor might not pick up on, and I now believe this to be the cause of the perforated water jacket in our original Alde boiler. All the precautions for galvanic corrosion to the outside of the boat had been taken, but this, in the internals had been overlooked.

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