Rusting unvented cyinder

[bblaukopf]

Just been in the airing cupboard, and my uv cylinder - Ariston Primo ITI 15

0, which is stainless steel with no sacrificial anode has got some interest ing swelling around the unused secondary return. There has obviously been a small bit of rusty water leaking out from there.

With the dust cover remove, it looks like this - poor picture, but basicall y there are several thin corroded layers that would just flake off if I sta rted scratching at it.

Interested in several things:

1) What's the outside bit? If that's steel it's seriously rotten - and sure ly the insulation would be on the outside anyway?

2) Any reason to believe this is immediately dangerous?

3) This is presumably seriously abnormal (or perhaps not, for Ariston, havi ng done some googling). I don't have proof of annual servicing so claiming under the warranty is unlikely to get me very far, but having read the serv icing guide, can't see how anything in it could be relevant to corrosion. T empted to claim under SOGA, but I suspect I'm on a hiding to nothing given I didn't purchase the damn thing myself, so I'd have to go after the plumbe r who fitted it. And it was nine years ago, though the whole reason for pur chasing stainless in the first place was that it was supposed to last....

4) What's a good make of unvented cylinder, preferably with a solar preheat coil so I can DIY a setup when I have some time...

[harryagain]

150, which is stainless steel with no sacrificial anode has got some interesting swelling around the unused secondary return. There has obviously been a small bit of rusty water leaking out from there.

With the dust cover remove, it looks like this - poor picture, but basically there are several thin corroded layers that would just flake off if I started scratching at it.

Interested in several things:

1) What's the outside bit? If that's steel it's seriously rotten - and surely the insulation would be on the outside anyway?

2) Any reason to believe this is immediately dangerous?

3) This is presumably seriously abnormal (or perhaps not, for Ariston, having done some googling). I don't have proof of annual servicing so claiming under the warranty is unlikely to get me very far, but having read the servicing guide, can't see how anything in it could be relevant to corrosion. Tempted to claim under SOGA, but I suspect I'm on a hiding to nothing given I didn't purchase the damn thing myself, so I'd have to go after the plumber who fitted it. And it was nine years ago, though the whole reason for purchasing stainless in the first place was that it was supposed to last....

4) What's a good make of unvented cylinder, preferably with a solar preheat coil so I can DIY a setup when I have some time...

That's an interesting picture. I suspect what you have is not a stainless steel tank but a vitreous enamelled one, ie plain steel with a fused glass coat. If the glass coat is damaged/faulty, the tank rusts. OR The other possibility is tha trusty water is running down inside the insulation from a leak elsewhere. Or the insulation is clad with a plain steel cover that's rusting somewhere.

[Brian Gaff]

Some stainless steel is ferrous though, as I've had stainless bolts go rusty. It admittedly takes longer, but the give away seems to be that you can pick them up with a magnet. Brian

[Andrew Gabriel]

There are several different grades of stainless steel, depending if you want to optimise for anti-corrosion, hardness, price, etc.

Also, stainless steel requires exposure to oxygen to become "stainless", or the chromium oxide protective layer doesn't form. I can't see in the OP's posting what the finish is, but the white layer sure isn't stainless steel.

[Chris French]

In message , Andrew Gabriel writes

I don't know anything much about these tanks, but I assume it consists of an inner watertight tank, insulation and then clad in another layer of metal?

Maybe the inner is SS and the outer cladding mild steel, with a paint/enamel coating. The rusting round the hole for the tapping suggests to me a small leak, (or maybe condensation?) causing the rusting?

[John Rumm]

The inner tank may be SS, then there will be a layer of insulation, and then some kind of outer covering. Looks like that is just painted mild steel in this case.

No. As long as the various safety valves are in good working order then there is no possibility of the tank being overheated to the point where it could flash boil on a pressure reduction. There is little or no energy stored in water under pressure (since its incompressible), so if it were to leak, that's all it does - it can't go bang.

You have no visibility of what the state of the actual cylinder is - you are just looking at the cladding. It could be that there is a small leak from the cylinder itself where the tapping penetrates it.

Telford, Albion, Heatrae Sadia (the market leader whose model Megaflow is used as a synonym for all other makes and models), Santon, Gledhill, Elston, IMI, & Vaillant to name a few.