HW cylinder leaking or condensation?

[Eponymous]

Hi.

I’ve just changed out a backup immersion heater on a copper vented cylinder.

I’ve leak tested around all the connections to the cylinder using blue paper towel which tends to stain orange with moisture.

After 24-48hrs of use not a trace of moisture.
However after a week or two I’ve noticed one or two very small spots/stains on the paper towel around the immersion heater and the coil inlet. The towel is bone-dry though.

Any ideas? Is this just condensation or could it be a bigger problem? I’m thinking I might need to replace the tank. I’m not sure how old it is. Tank is in the airing cupboard.

Cheers .

 

[Maryplumb]

If the original immersion was leaking water may have run under the insulation?
Not sure what you mean by the towel being spotted but still bone dry.
Condensation occurs on cold surfaces.

 

[Eponymous]

If the original immersion was leaking water may have run under the insulation?
Not sure what you mean by the towel being spotted but still bone dry.
Condensation occurs on cold surfaces.

Hi.

Yes it’s certainly possible it’s leftover water.

What I meant with the towel is it’s got marks on it as if it’s been wet in places - orange stains indicating water has soaked into it at one point. However when I checked the towel it was completely dry.

I’m aware condensation occurs only on cold surfaces however the hot water cylinder will cycle between hot and old depending on if the hot water circuit is on or not. So perhaps it is accumulating moisture at night when it is being filled by very cold water from the attic?

 

[Maryplumb]

Well the cold feed and the bottom of the cylinder might get cold but unlikely higher up. Guess you will just have to monitor it but I think it's unlikely you need a new cylinder.