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Posted By Topic: HWC element

Nov 02 2013 09:10

My in-laws have had the second element pulled from their HWC in 4 years, completely corroded through and leaking out the terminals.
It is one of those Solarhart horizontal roof mounted cylinders with a solar thermal panel.
I think they will be ripping it off ASAP, but I am still interested to know why this would be happening.

Any theories?

Nov 02 2013 09:29

One likely cause is use of incorrect element.
Elements need to match the cylinder ; eg nickel plate for copper cylinders, tin plate for glass-lined steel. inconel is normal for stainless steel cylinders.

The other thing to look at is water quality, hard water needs different element.


Nov 02 2013 10:59

Sounds like electrolytic corrosion and the element may be acting as a sacrificial anode.?

Is the array earthed or floating or somewhere in between.

Best suggestion would be to note the make/model size of the solar system and the same for the heating element.

Check for earthing, pipe work etc.

Contact Solarhart and ask about known corrosion and incompatibility issues.

Nov 03 2013 19:02

Thanks for the ideas.

All the work to date has been done by solahart so I would assume that they are using a compatible element in their own cylinder. That said, there is a quote about assuming...

I know the water is hard where they are but they never had issues like this with their old HWC system.

I will look into the earthing when I am out there next.

Nov 03 2013 20:09

Some solar HW have a built sacrificial anode. Something like a 500mm brass or aluminium rod that bolted into the cylinder and was earthed. It prevented stray earth currents finding other routes to earth and corroding cylinder fittings etc.

It was often used on copper piped systems where the external copper pipe may join to internal plastic pipe or where the circulation pump in and out fittings were plastic and acted as an earth break. It was a functional earth as opposed to a safety earth.