intermittent slow leak from cold tank?

[hba]

Hi all

I have a cold tank (polythene, about 30 years old) and recently there was a pool of water around and under it on its plywood platform. There is no sign of leaks from outlet, overflow etc pipes. A few days later it had dried up quite a lot. A few days more and there was new water, but less than before, and now a few more days after that it seems to be drying out again. I'll check if it happens when it rains but there is no obvious staining or damp on the roof above it.

My question is, do cold tanks spring microleaks that might let out half a cup of water every few days, then stop for a while? I can find nothing like this here or on Google.

And if so, what do people think about using a non-viscous silicone 'Seek n seal' type product, draining the talk and painting it inside?

Many thanks in advance

 

[Stigster]

Intermittent leaks from the tank connectors is unlikely but possible. Strange things do sometimes happen with temperature changes in the loft. However, if it is truly intermittent, in my opinion I would want to look at the cold inlet valve as a possible culprit.

There's a couple of things that could be happening. Pressure fluctuates during the daytime and can certainly increase at night time when there is low demand on the supply system. It is possible that the connection to the inlet valve only leaks at night.

The other possibility is that again, under certain conditions the cold inlet valve lets by, overfills the tank and drains through the overflow warning pipe. The overflow pipe may have a leak on it somewhere near your tank stand or where the overflow warning connects to the tank.

Intermittent leaks can sometimes be a pain to find but those are the main causes of intermittent tank leaks that I can think of. I would regularly monitor the storage tank using a paper towel (preferably the blue stuff as it shows water very well but any paper will do) and wipe around all surrounding joints, fittings and connections. Hopefully something will show that way.

 

[SimonG]

As above, overnight when there is no hot water use the inlet valve could be passing and water through the overflow which is leaking onto platform.

This why I like blue roll, wrap some bits around where you think the water is coming from. Will sharp show you where it's coming from.

 

[centralheatking]

Hi all

I have a cold tank (polythene, about 30 years old) and recently there was a pool of water around and under it on its plywood platform. There is no sign of leaks from outlet, overflow etc pipes. A few days later it had dried up quite a lot. A few days more and there was new water, but less than before, and now a few more days after that it seems to be drying out again. I'll check if it happens when it rains but there is no obvious staining or damp on the roof above it.

My question is, do cold tanks spring microleaks that might let out half a cup of water every few days, then stop for a while? I can find nothing like this here or on Google.

And if so, what do people think about using a non-viscous silicone 'Seek n seal' type product, draining the talk and painting it inside?

Many thanks in advance

Check the water level in the tank at different times. Or look for the tide mark it is quite likely the ball valve needs setting lower or servicing and the intermittent water is from the overflow. You can test this by deliberately holding the ball down till water level rises up to overflow then check around for damp
Centralheatking

 

[hba]

Thanks both. It just doesn't look like there's ever been water from tank connectors. I didn't try blue paper but felt all around the pipes and looked for damp on my hands. I since got some washable children's felt pens and painted lines on bits of sticky label and stuck them under and on everything going into the tank. So any drop of water will show even after it's dried.

There's a hot water expansion pipe that may be the culprit though that also always seems dry. I'll also check after rain in case the roof is the offender.

But it looks like nobody seems to come across polythene tanks themselves leaking this way.
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Check the water level in the tank at different times. Or look for the tide mark it is quite likely the ball valve needs setting lower or servicing and the intermittent water is from the overflow. You can test this by deliberately holding the ball down till water level rises up to overflow then check around for damp
Centralheatking

Thanks centralheatking (like the avatar). There is no tidemark above the current level, well below the overflow. I'd stuck my sticky labels inside to check the level didn't rise until I realised it would be a bad thing to fall off and get into the booster pump. I'll certainly do as you suggest if it happens again without the cause being clear.
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I think I've found out what's happening. I've found chalky deposits on the top edge of the tank, where the lid clips on, in one corner. I think the tank refilling is somehow splashing up onto the lid, and the water is running to the corner and dripping down on the outside. I don't know why it's only every few days. Best guess is it only happens when the tank level is low (daughter having a mega-shower).

I'm going to have to rig up some sort of drip groove round the underside of the lid so that its lowest point isn't actually outside the tank. The lid is slightly convex, a bit domed, surely a bad design fault.

Thanks again to all who replied.

 

[centralheatking]

Thanks both. It just doesn't look like there's ever been water from tank connectors. I didn't try blue paper but felt all around the pipes and looked for damp on my hands. I since got some washable children's felt pens and painted lines on bits of sticky label and stuck them under and on everything going into the tank. So any drop of water will show even after it's dried.

There's a hot water expansion pipe that may be the culprit though that also always seems dry. I'll also check after rain in case the roof is the offender.

But it looks like nobody seems to come across polythene tanks themselves leaking this way.
[automerge]1580402454[/automerge]

Thanks centralheatking (like the avatar). There is no tidemark above the current level, well below the overflow. I'd stuck my sticky labels inside to check the level didn't rise until I realised it would be a bad thing to fall off and get into the booster pump. I'll certainly do as you suggest if it happens again without the cause being clear.
[automerge]1580415455[/automerge]
I think I've found out what's happening. I've found chalky deposits on the top edge of the tank, where the lid clips on, in one corner. I think the tank refilling is somehow splashing up onto the lid, and the water is running to the corner and dripping down on the outside. I don't know why it's only every few days. Best guess is it only happens when the tank level is low (daughter having a mega-shower).

I'm going to have to rig up some sort of drip groove round the underside of the lid so that its lowest point isn't actually outside the tank. The lid is slightly convex, a bit domed, surely a bad design fault.

Thanks again to all who replied.

Turn the lid upside down and if it works tape it down Centralheatking

 

[hba]

Now that's an idea CHK. I'm going to try putting a weight in the middle too. Problem is the space is so tight that the lip of the lid one side is wedged in against the roof timbers.

What I was thinking was to fix a flexible tube round inside with silicone. But I'll try anything that works.

For now I've just propped up that corner so the water shouldn't run in that direction.