Really, really odd - dampness of some sort

Having something of a nightmare currently, and all of it seems to centre around damp/moisture and I am somewhat chasing my tail. Bit of background to all of this in this post - if you want to skip to today's problem, go to post 2!

First up was the leak under the bath that came through the kitchen ceiling - initially, I had that pinned to busted silicone around the bath and the base of the taps, so I renewed all of the silicone.
The leak came back with a vengeance so the bath panel was removed, overflow and and waste trap was definitely leaking, so I replaced all of that.

Next, attention turned to windows/doors and even walls where condensation was a problem and mould was starting to form. At the same time, we had the dual problem that we had lots of washing taking days to dry and in some cases not drying at all and having to be re-washed. I was blaming the washing and lack of heating for the dampness, so did a chunk of research and worked out that our 10 year old tumble dryer (sitting unused for a year because of the cost of running the thing) was a condensing one but not a heat pump one. Samsung were doing a deal where we got £150 to trade the old one in and a new heat pump tumble dryer on interest free for the princely sum of £18 per month. That was installed a week or so ago and is one of the best things we have done - windows etc downstairs are now all but dry and we are able to dry a large load of washing for pennies.

Today, the next stage unfolded....

 

We had a stain on the carpet at our bedroom door. This stain has been there for around a year on and off; cleaning the carpet would see it go for a while, but slowly it would come back. More recently, one has appeared at the top of the stairs too - plus, the door on our daughter's bedroom seems to have swollen as it rubs on the frame when it never has in the 11 years we've been here.

We were getting the carpet cleaner out to properly clean up after my accident yesterday, so decided that whilst it was out we may as well have another go at the stain - but first, lift the carpet to see if we could work out where it was coming from. I really wish I hadn't bothered!

The underlay at our bedroom door and at the top of the stairs felt and looked really damp - but also had a strange sort of oily/greasy/stickyish feel to it. The carpet on top was dry.

The floorboards underneath also had the look of damp about them, but again had this sort of oily feel to them. So, I set to lifting some to see if I could find the source... nothing, the underside of the boards were completely dry! I tried quite a few different boards that would lift - all the same, all dry. Checked the central heating pipes - no leaks visible and in fairness it hasn't lost pressure either, as it would do if there was a leak somewhere.

Hot water tank checked, all the pipes in the airing cupboard checked - nothing.

The underlay is all but knackered, so there is two large chunks that I've simply binned as it wasn't even worth drying out - I will simply replace it. For now, I have laid the carpets back down loosely, have walloped the heating up and have dug out our air con unit and I am running that as a dehumidifier, but I am completely stumped.

There is no water pipes under that part of the floor, the walls are all internal walls.

Anyone came up against anything like this?

 

Doors and walls are dry - we've fairly recently redecorated the whole house, so it would be easy to see if that makes sense. I need to re-do the kitchen ceiling thanks to the bath, but that was clearly a visible leak once I got under the bath.

The condensation we had with the washing indoors was really bad downstairs - but that has gone now we don't have the washing there.

 

We do - two dogs, both very well housetrained. Carpets are dry too, it is only the underlay that was wet, and no smell of pee.

 

I wondered if it would be the underlay breaking down - the bits where it was wet to the touch did feel a greasy/stickyish sort of wet, and the bottom 'waffle' bit was utterly shot. I have literally cut the lot away and binned it as nothing was going to save it.

 

That could well be it then! The underside of the floorboards are completely dry as is the carpet above and the underlay/carpet will be 15 years old if it is a day. Oh well, I will replace those two chunks of underlay and see what it does for us then.