Leak, but no leak?!

[womble69]

I've posted this query here first, because I think that plumbers may have come across the problem before.

I've bought a small 1930's terrace. New CH and boiler gone in months ago. Most if not all pipework is new. System runs fine, no pressure loss. Heating is not run very much because the house is naturally fairly warm, although it is prone to cold spotting.

I noticed that the surface of some of the floorboards in one upstairs room have marks that suggest a water leak, so I lifted the boards. The boards appeared dry underneath. I did find definate traces of water on the ceiling (top surface, underneath floor). I could find no water on pipes themselves. I wrapped some pipes in newspaper and checked later, but bone dry. One piece underneath a pipe did develop a very small wet patch.

This is where it gets weird.

The marks on the floorboards do not necessarily tally with where the pipes lie. Even stranger, where I found the wettest bit was where there are no pipes at all.

So, where on earth could the moisture be coming from? At first glance, it's a leak, yet I cannot pin anything down and there are contradictions. Is it possible for cold pipes under the floorboards to drip condensation? The house is prone to some quite cold spots, and as I say, the heating is not run often.

 

[libby lou lou]

For condensation to form, the moisture must be around the cold pipe, it has to come from somewhere.
Maybe more ventilation/insulation is needed, cheapest option?

 

[leakydave]

Does either your dog or your cat need to be taken to the vet?

 

[womble69]

Does either your dog or your cat need to be taken to the vet?

Ha. No dog or cat. The moisture is under the floorboards.

What's so strange is that I couldn't find any moisture on the pipes themselves, and there was wet where there were no pipes at all. Is it possible for the underside of floorboards to get cold enough for condensation?

 

[leakydave]

It is possible for copper pipe to pinhole, a very fine hole can spray water quite a long way, often in a virtually invisible jet. I have seen it myself a few times.

It is worth taking a good look and running your hands along pipes and poking a powerful torch under the floor and looking carefully!

 

[gasbanni]

System runs fine, no pressure loss.

No pressure loss no heating circuit leak.

Condensation on cold water pipe perhaps ?

Building up and dripping ?

 

[womble69]

Yes, a pinhole was my first guess, but I can't see anything. The pipes and underside of the floorboards are dry.

I even wrapped the pipes in newspaper and checked later, but nothing! Just these weird patches of what seems to be water on the top surface of the ceiling boards. Some of the joists are stained and apparently moist from water - looks like capilliary action drawing water along.

What's even stranger is that the blotches of apparent water appear where there are no pipes at all.

One thought though - do plumbing folks use anything that might have been spilt under the floor during the installation of the CH and later be mistaken for water. Some sort of flux or similar maybe? When I rub my fingers in this stuff it has a distinctly oily feel, even though it's water soluble.

I've taken out old iron electrical conduits that were left between the floors. Some of those were very cold and had some rust. But again, there's blotches where there's nothing but wooden beams!