Mould on wooden floorboards under box

[ree]

OP,
Thank you for the detailed & intelligible plan view.
The old damp work might have been due to moisture meter readings in corners - these corner MM readings are often readings of condensation damp without the spots?
The party wall damp might have been connected with the missing chimney breast?

You show an air brick venting the kitchen floor - so the dividing wall behind the rad has vented floors on both sides - pics of the new damp signs might help?
Hallway sub-areas are often unvented?

Did the "damp specialist's" hack off & renew the damp defective plaster - & what kind of chemical DPC was used?

 

[livinginhope]

That's interesting. Damp near the kitchen.

No doubt the kitchen contains water pipes and drains. Does it have a concrete floor?

Tiled. I don't know what's under the tiles (but I suspect wooden floorboards - it's an old house and I see no reason to think they'd have built the kitchen any differently from the rest of the house)

Have you got a water meter?

Out in the street. Under a manhole so I don't know how to access it. Are you thinking of using the water meter to see if there's a leak? (FWIW that is my suspicion for the damp patch above the radiator, mainly because I cannot think of anything else that could cause a patch that high up). Unfortunately, there's no way to investigate without basically ripping half the kitchen out.

If you drew a line between the external stopcock (where the front gate used to be when the house was built) and the internal stopcock (where the sink used to be when the house was built) would it pass under the hall floor?

The internal stopcock either doesn't exist or is inaccessible. Plumbers have given up looking for it in the past. (I know, I know. Old house. ). But a direct line from the kitchen to the external stopcock would pass under the hall floor, so that's where I'd expect the water supply pipe to be.

Does your boiler have a pressure gauge?

Can you obtain a young person with sharp hearing?

Yes, and boiler pressure is normal. A person with sharp hearing? I'm intrigued... to what purpose?

 

[StephenOak]

Out in the street. Under a manhole

Do you actually mean a manhole? They are large (18" by 2'6") whereas the covers for water meters are much smaller, no more than 6" on a side. Water meter covers are quite easy to lift.

 

[JohnD]

A person with sharp hearing? I'm intrigued... to what purpose?

A leak in a water supply pipe makes a faint hiss. You hardly hear it, and it disappears from notice. But when it stops and starts, in a quiet house, , as when the external stopcock is turned off and on, a person with good hearing notices it.

Young people have better hearing than old, especially for higher frequencies.

Water supply pipes commonly leak after 50 to 100 years.

If you have no internal stopcock, and a leak, it will be less easy to determine whether it is under the hall or kitchen floor, or elsewhere in the house.

It is common for the hall and kitchen to have solid floors.

It is harder to dig up a pipe buried in concrete.

 

[ree]

OP,
It might be useful for you to know that concrete flooring was not common in terraced housing - hence, the suspended kitchen floor airbrick shown in your post #13 pic.
Hallways were typically suspended floors.

Its not at all common for pipes to leak after 50 to a 100 years - certain pipes in certain surrounding conditions might be more liable to leak but its not common to all water supply pipes.

As regards the external & internal stop taps then its best to locate both of them, and then operate them - when you future need either of them you might need them in a hurry.