Anode query

[Gone West]

I have an enamelled DHW UVC in my Genvex which is fitted with an anode. The manual says the anode should be checked every two years and the expected lifetime is 2 to 5 years so I took it out today after 2 years 9months and it doesn't look much different to the new one, just a bit pitted. The manual says it should be replaced when down to 10mm diameter. The dimensions of the new one are diameter 33.5mm and length 469mm and the removed one 31mm diameter and 440mm long. Calculating the volume of magnesium lost from the anode I reckon it to be about 1/4 of the original. If that's the case the anode should last around eight years. Does that sound right? I have fitted the new anode and don't want the faff of draining the tank down unnecessarily so is it reasonable to to assume it should last at least five years.

 

Edited October 1, 2020 by PeterStarck

[Onoff]

Doesn't the surface area decrease with time so the corrosion accelerates? 

 

Is it worth descaling every time with say a circa 40% phosphoric acid?

[Gone West]

The surface area would decrease with time but presumably the material would be lost at the same rate as a volume. I guess the most loss from the anode which is at the threaded end is because the enamelling around the anode hole flange isn't complete.

There's no scale formed. I shone a torch into the tank and it's clean but it looks like the anode has a soft coating which may be NaCl from the softener.

[Thedreamer]

Hi @PeterStarck can I ask do you live in a hard or soft water area? Also how much do these cost? 

[Gone West]

10 hours ago, Thedreamer said:

Hi @PeterStarck can I ask do you live in a hard or soft water area? Also how much do these cost? 

The water is very hard here and the softener I use removes all the hardness. The anode for the Genvex is magnesium and cost £102 all in from the UK, although they are cheaper from Europe.