Rust from shower (hot water side)

[John Smith Esq.]

Hi all,

I've provided photos below.

My shower mixer has the hot and cold water pipes going right through the wall and into the cubicle from the boiler cupboard. There are two round screw caps that enclose the part where the copper pipes go into the mixer. I've noticed rust stains below the hot water side on the wall of the shower cubicle. When I unscrew the circular cap, a load of black rusty water comes out... perhaps 25ml. (Last time I did this was about a month ago). The same isn't happening on the cold side or not as severely so it isn't noticeable.

What is the reason for this? Is water from the shower head getting behind the circular cap from outside and then causing some corrosion because it is hot in there (I have the caps screwed quite tightly against the wall.) Or is there a leak inside where the copper pipe connects with the mixer, causing water to sit inside the cap?

I was going to put silicone around the outside of the cap, to solve the first problem of water getting in from the outside, but if the water is coming from inside the cap, this solution wouldn't help and might make things worse if the rusty water can't escape.

There is no leak evident behind the shower wall or in the boiler cupboard.

Thanks for any advice you can offer.

 

[terryplumb]

I would remove the shower valve and chrome covers to investigate what's going on.

 

[John Smith Esq.]

So this isn't typical?

 

[Burnerman]

I guess you have a leak where the hot supply joins into the shower bar.......not so unusual, some of the connecting methods aren't as good as they could be.
I'd doubt if the water was rust though - everything in there should be brass or plastic so I reckon it's just dirty water.
If you feel inclined, you could inspect the problem if you enlarged the holes where the pipes exit the boiler cupboard?
John

 

[Burnerman]

Not typical, and not desirable....if it's coming from the back it could be dripping within the pipe void?
John

 

[terryplumb]

If I had to make a guess ,I would suspect fixing screws are rusting. As said above there shouldn't be anything behind the shower valve that can rust.

 

[John Smith Esq.]

Alright chaps. I've added some photos.

Some further information. The screw cap where the rust is coming from actually has a gap on both side of the central hole. So water could be getting into the cap through that when the shower is in use. Hot water so steam. There is some kind of brass type fitting that has some green corrosion on it. And it's definitely rust inside cap.

Thoughts?

 

[Burnerman]

For sure, shower splash will definitely be getting in there.
If you can isolate the shower and then remove the shower bar then you'll see better. From your original first pic, it would be easy enough to install isolating valves in the pipe work, just make sure they are the full bore type.
Still no idea about any rust though - unless its the plating on the cap itself that is to blame.
John

 

[terryplumb]

You can easily remove the shower valve to see what's behind it. It's either screws rusting or silicone reacting with the brass mounting plate ,the only 2 things I have ever seen that cause the symptoms you have.

 

[dilalio]

Thoughts?

As said above, I'd suspect steel screws rusting on fixing plates - should be stainless or brass but who knows!

I'd take the valve off, remove the shrouds, apply silicone Al around the top and centre of the fixing plate and pipe, and up to the top of where shroud circumference sits, but leave bottom clear so any water can drain out.

Whilst you have the shrouds off, pop the valve back on and run it to check for any leaks on supply but I doubt it's this.