How to fix this leak from a hot-water tank?

[David001]

We've just discovered there's a long-established leak from a pipe attached to the side of our hot-water tank.

 

It seems the leak is only slight because there's no pooling of water, although the surface of the board beneath the tank feels wet.

The encrustation down the side of the tank suggests the leak has existed for many months.

 

The nearest plumbers are situated about 25 minutes' drive away, so before we consider asking one of them to come and help, we'd like to know:

 

• what's involved in fixing this leak,
• and whether I might fix it myself (I'm handy with spanners etc., but have no plumbing skills).

 

I can see that I could unscrew the vertical pipe from the short horizontal one which enters the tank, but what would have to be done after that?

The short horizontal pipe at the site of the leak has a plastic adjustment knob on the end of it.

 

The first photo shows the front of the tank, and the second is a close-up of the position of the leak.

 

Thank you for your advice.

 

 

 

[Iceverge]

You need to establish what's leaking first of all. 

 

If it's beside the threads of the fitting it's pretty straightforward. 

 

Remove the fitting , clean all h

Threads with a wire brush and use some hemp and plumbers compound to re attach. 

 

If it's the tank leaking you probably need to replace it unless you're good at brazing. 

 

 

Have you checked the pressure and temp relief valves are working ok recently? This could be a symptom of an over pressurising tank. 

[JohnMo]

  On 20/03/2025 at 17:30, Iceverge said:

you probably need to replace it unless you're good at brazing

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braze - no

This is a pressure vessel don't mess with them. Fix leak as discussed about. If the cylinder leaks replace it.

[David001]

  On 20/03/2025 at 17:30, Iceverge said:

<< You need to establish what's leaking first of all. >>

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@Iceverge, thanks for your ideas.  It's water that is leaking and I believe it must be initially coming from the inner tank.

When I look closely at the visible source of the leak I see that the brass fitting appears to have passed through a thickness of yellow insulation foam/wool.

The brass fitting is not sealed to the outer (visible) "skin" of the tank.  The large plastic disc appears to be as aesthetic as much it is meant to cover up the tiny amount of open space around the brass fitting as it passes through the outer skin.

So I imagine that the brass fitting is meant to be securely attached to the inner skin, but it isn't tight and so water is leaking into the space between the two metal skins.

Perhaps the insulation between the two metal skins is not dense enough, or waterproof, to resist the incoming water, in which case the layer of insulation all around the tank may be saturated with water.

 

  On 20/03/2025 at 17:30, Iceverge said:

If it's beside the threads of the fitting it's pretty straightforward. 

Remove the fitting , clean all h

Threads with a wire brush and use some hemp and plumbers compound to re attach. 

If it's the tank leaking you probably need to replace it unless you're good at brazing. 

Have you checked the pressure and temp relief valves are working ok recently? This could be a symptom of an over pressurising tank. 

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I can't see that I can clean the threads attaching the brass fitting to the inner skin without taking off the top of the tank somehow, as well as draining the tank, so as to access the fitting from inside the tank.

 

I have no idea how to check "the pressure and temp relief valves", but take your point that the leak could be due to an over-pressurising tank - although if water can pass through, as it clearly is, I believe it would still seep through no matter what the pressure is.  But I have little idea about these things.

Edited March 21 by David001

[David001]

  On 20/03/2025 at 18:21, JohnMo said:

braze - no

This is a pressure vessel don't mess with them. Fix leak as discussed about. If the cylinder leaks replace it.

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@JohnMo, for the moment, I am gently cleaning up the outside of the tank so that I will be able to place a tray under the tank and monitor just how much water is dripping out.

I put a tray under the tank last night and this morning found it still dry.  But until the encrustation is removed I can't be sure that droplets of water aren't still coming out but are then settling within the encrustation.

 

I'm beginning to think that we don't have an urgent problem, but unless a plumber can get inside the tank to stop the leak through the inner skin, a new tank will eventually have to be fitted, which will no doubt be a costly and tricky operation.

Edited March 21 by David001

[Iceverge]

 

Have a look at this video. 

 

A mandatory annual check I think in the UK. It should explain the T&P valves in there somewhere. 

 

Most tanks have male threads as part of the cylinder.  These project through a layer of polyurethane foam (insulant) and a lightweight metal skin ( only there to protect the insulation) . 

 

Insulation and outer skin will have nothing to do with your leak. 

 

 

 

If you screw off the offending fitting then you may be able to clean it and reassemble with appropriate sealing. 

 

Yes you will need to drain the tank down to do this. 

 

If you're not confident it might be worth summoning a plumber as the fitting wouldn't be too hard to overtighten and crack the tank. Likewise the G3 requirements of an UVC are technically pros only in the UK as far as I know.

 

 

 

[David001]

@JohnMo and @Iceverge,

 

I've now cleaned away a lot of the encrustation on the side of the tank and can now more clearly observe what's going on.

I've made sure that any water that escapes through the hole near the top of the tank will dribble directly onto a plastic lid I've placed under the tank.

 

I put the lid in position 30 minutes ago, and already an oval of water has formed on the plastic lid, showing how much water is seeping from the tank during a 30 minute period.

It's more than I was hoping for, suggesting I need to get this leak fixed sooner rather than later.

 

If at the leak point I remove the plastic disc around the brass fitting that passes through the outer metal skin of the tank, and if then I were somehow able to unscrew the brass fitting from the inner metal skin, I believe the hole in the outer skin will be too narrow to allow any work to take place through it.

 

What is the likely distance between the inner and the outer skin?

In other words, how thick is the insulation foam between the two skins?

 

Do you have experience of, or thoughts about, the "Santon Premier Plus Unvented Indirect Cylinder"?

 

Thank you from a 70-year-old who has no experience of plumbing! 🙂

[David001]

@Iceverge, many thanks for the video, and for the pic of a tank.

 

Please could you have a look at the further close-up below, which shows my tank's leak point?

 

It seems that the thin grey plastic disc, which I thought was more aesthetic than anything else, is the outer part of a grey circular plastic pipe which enters the opening in the metal skin of the tank.

Do you think that that grey plastic is "hiding" a metal thread protruding from the skin of the tank, as in the photo of the tank which you have just posted?

 

[Iceverge]

That very much looks like a male thread protruding from the tank. 

 

This means that the brass fittings ( I think it's a T&P valve) is female so should be pretty straightforward to clean threads . 

 

 

However .......from the Brochure of your particular brand of tank it appears to come with that brass fittings already in place.

This could unfortunately serve as  something to manhandle and bash during transit and installation so there is a lightly hood that it will have cracked the tanks. 

 

 

Can you determine from the above joint where the leak is coming from? 

 

Is it following the line of the orange or pink arrow? 

 

 

 

 

[David001]

@Iceverge, thank you so much for your helpfulness.  

 

With that grey plastic disc in position it's difficult for me to see whether the leak has come from behind it or whether water dropped onto the face of it from the brass fitting above. 

 

But you have given me enough reason to have a go, hopefully today, at, firstly, trying to drain the tank, and then seeing if I can unscrew the brass fitting in order to clean up the threads and apply a little Plumber's Mate.

 

 

[Iceverge]

You'll need hemp too.

 

Scrape the exposed threads with a hacksaw blade to get it rough enough to get the hemp to stick. And apply the plumbers mate as you go. It'll end up the same consistency as hair matted in butter. 

 

It's a fiddly job the first time you do it. 

 

There's a balance to getting the fixture tight enough but not too tight to crack the tank. 

 

Beware that if it goes wrong today ( Saturday) you might be without hot water for a few days. 

[David001]

@Iceverge, thanks for the advice above which I have only just found - after four hours (mainly spent working out how to empty the tank of all its water!), and managing to unscrew the horizontal brass piece entering the grey plastic collar.  Please see the photo below.

 

The thread of this horizontal brass piece is deeply encrusted with calcium or some other white deposit, perhaps including some degraded plumber's mate. 

 

The stiff grey plastic collar has a thread on its inside!  By pushing my finger as far as I could extend it into the plastic collar, I found that the thread eventually ends and the plastic becomes smooth and continues inwards beyond the end of my finger.

 

So the horizontal brass section, which I unscrewed from the inside of the grey plastic section, is male, and the grey plastic collar is female.  I had expected the brass section to be female, and had expected to find that it was attached to a male piece inside the grey plastic collar.

 

Anyway, presumably the long thin sensor attached to the brass fitting sits constantly within water, explaining the leak which has been occurring between the grey collar and the brass piece.  I don't dare to extract the grey plastic collar, as it seems to me that it must be bonded to the inner skin of the tank.  I suppose that it is possible that being plastic the collar may nevertheless have cracked, so that water has escaped under the collar rather than inside the collar.  Although perhaps it's been passing out through both routes.

 

I am cleaning the horizontal brass piece and the interior of the grey plastic collar using vinegar and occasional gentle rubbing with a toothbrush. This may take a number of days.  Then I will try screwing the brass piece back in position, using some plumber's mate and then wait to see if the leak has been stopped.

 

What is the purpose of the brass piece with the sensor attached?  How does it work?

 

And is there anything else that I ought to be doing - or which I not to be doing?  😱  I have no experience of plumbing, so all of this has been a little "terrifying". 😁

 

Thank you.

 

 

Edited March 22 by David001

[Iceverge]

Pics of this plastic collar please.
 

I'm guessing it's a screw in bushing reducer to take the thread down to an appropriate size. 

 

You may be able to screw it out and replace it.

 

If you want to have a go as is by all means a do but be careful with applying hemp liberally to the thread as it may crack the plastic. 

 

The T&P valve provides a safety blow off in the situation the tank overheats or over pressurises. 

 

You can clean the brass threads relatively aggressively with a wire brush. 

 

By the way I'm not a plumber so beware internet stranger advice!!! 

 

 

 

 

[David001]

@Iceverge, thanks for all your advice.  The brass unit was thoroughly cleaned, and then it's thread was coated with plumber's mate, and then carefully repositioned, and now all is well. 👍

[Nickfromwales]

  On 25/03/2025 at 11:26, David001 said:

@Iceverge, thanks for all your advice.  The brass unit was thoroughly cleaned, and then it's thread was coated with plumber's mate, and then carefully repositioned, and now all is well. 👍

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Happy days. 
 

BTW, the grey outer collar is cosmetic, and the female threaded union you just refitted that to is welded to the tank. I looked at the MIs and the tank is stainless, so no other harm will have happened other than the bits of corrosion on the steel sleeve at the base, but again cosmetic. 
 

All good!