Electrical hot water systems incorporate a device designed to reduce corrosion on the internal metal components. A bar made of magnesium is installed in the base of the system, its correct name is a Sacrificial Anode...you will also find a sacrificial anode of the skeg of an out board boat motor. The idea is that the anode bar, which is easily replaced, will corrode thereby reducing corrosion within the water tank, or the outboard outboard motor. Anode bars should be inspected regularly, especially if water with a high concentration of minerals, ie, outback bore water has been used...six monthly inspections are recommended....click on the photo below and see how to do this with a slide show.
Warning...ensure mains power and mains water is disconnected from the RV before carrying out this maintenance work.
In this case the HWS is a US made Suburban brand, a very popular system used in the majority of Australian caravans and RV's...yours may be different but regardless it will still have a sacrificial anode installed somewhere...you may have to check your user manual or contact the manufacturer if you are unsure.
Before proceeding you will need to relieve the system water pressure, do this by pulling the drain lever towards you, obviously any water pumps need to be deactivated and there should be no hose connection to the RV...ensure also that you have shut down the 240v power connection. (you will be spraying water around this area during this operation)
The bar is installed behind a large hex head at the base, you will need a 27mm socket to remove it....water and gunk will come out of the hole when the bar is removed...allow it to drain completely...insert a hose and flush, do this several times until the water comes out clean.
You might also be interested in a flusher device I made that can also be used here....click to see
The bar on the left is new, the middle one 10 months old and the right hand one about also about 10 months, the degree of wear will depend on the water quality, in this case a mixture of bore and town water had been used. When you re-install the bar ensure you apply thread tape, start it turning by hand, you really do not want to cross the thread here.
This bar is only around 50% worn yet due to the relatively cheap cost of these things I would consider replace this one had I gone to the trouble of inspecting it. I brought mine online, genuine Suburban units will cost around $15 each plus p&p.