Condensation on LAGGED expansion pipe in the loft

cgkstevenson · 29 Mar 2020

ALL the pipes in the loft are lagged with the standard polythene sleeves. There is one vent pipe into the cold water tank which is dripping with condensation inside the sleeve. The pipe rises from floor level to the height of the tank , about 12 feet since the tank is right in the apex of the roof. Removing the sleeve shows a fair amount of copper corrosion, and it's wet. I removed the sleeve at the bottom of the pipe hoping it would air dry there, I think I really need to remove the sleeving all the way up. It's so bad I have a drip tray underneath which I have to regularly empty, and I can't see that the vent is ever used, so no water in it. I'm supposing it is a vent from the hot water tank, but that is on the floor below and a good 30 foot run of pipe up, then along the floor till coming round to the tank.

Suggestions ?

CBW · 29 Mar 2020

Sounds like it’s pumping over slightly. Remove lagging for 24 hours and see if it still occurs.

cgkstevenson · 29 Mar 2020

There's no pumping . It's an open vented system . The pipe runs 4 foot into the ceiling then travels along the loft floor for 24 foot (across the length of the loft then right angle into the centre) , then another 12 foot up to overflow into the cold water tank. So that's a very long expansion run until any water might overflow into the tank, which I doubt ever has happened.

JohnD · 29 Mar 2020

is the water in either tank getting warm?

Have you got an immersion heater? Is the tapwater surprisingly hot? Or do you have downlighters, or no effective extractor fan, in the bathroom?

cgkstevenson · 29 Mar 2020

This is the pipe. I removed the lagging so you can see it's wet and also corrosion

It's in the unconverted part of the loft space. No , no warm water ever gets up the pipe and into the tank. Water is not over hot. Pipe is COLD. 36 foot run of pipe from the hot water tanks to here...

endecotp · 29 Mar 2020

cgkstevenson said:
The pipe runs 4 foot into the ceiling then travels along the loft floor for 24 foot (across the length of the loft then right angle into the centre) , then another 12 foot up to overflow into the cold water tank. So that's a very long expansion run until any water might overflow into the tank, which I doubt ever has happened.

Isn’t the normal water level in that pipe at the level of the water in the header tank? I.e. all of that 24 feet is full of water?

cgkstevenson · 29 Mar 2020

now that makes sense ... since it's open then you'd expect the levels to equalise .

So maybe the answer is to dry off the pipes, re-apply the lagging but make sure it's a tight seal .

terryplumb · 29 Mar 2020

Fit thicker lagging .

oldbutnotdead · 29 Mar 2020

If you use the normal slit foam stuff, consider taping the joins and slits with the foil tape used on insulation boards.
As an aside, warm waterladen air is getting into your loft somehow, you might want to trace and seal the air leaks from the living space into the loft, they'll be costing you money as well as potentially causing damage

cgkstevenson · 30 Mar 2020

Not condensation at all , but pinholes ...

I was drying off the pipe preparing to bind and re-lag and kept finding damp bits, and realised there were places where tiny amounts of water were coming out. And these were not in the corroded areas, one near a soldered join.

The whole pipe run is a mess anyway, a couple of inline soldered joins, so I'm just going to cut it all out and replace.

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Condensation on LAGGED expansion pipe in the loft

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