My second instant water heater is rusting

[jacoscar]

I just noticed a drop of water under my instant water heater (Ariston Aures Slim Instantaneous Water Heater 9.5kW)

I opened it and I found it rusted inside
I previously had a different brand that died by the same fate (https://www.redring.co.uk/product/rp1-powerstream-95kw)

Is it just bad luck or they are all crap?
The first one lasted 3 years and this one just over 1 year

 

[ianmcd]

That isnt rust

 

[jacoscar]

That isnt rust

What is it? Anyway there is a small leak as I found drops of water inside

 

[JohnD]

Looks like a combination of white limescale, and green copper corrosion.

 

[jacoscar]

Whatever it is is cause by a leak, isn’t it?

 

[JohnD]

Clean it off with a green scourer, blow talc on it, watch. The leak will leave a trail to show you where it comes from.