ᐅ Walls painted, left unheated for years – now showing stains.

Complete renovation of an old farmhouse. Gas, water, and electricity – everything has been replaced. We finally have heating after 3 days! The walls we painted about a month ago are now showing strong discoloration and spots, as you can see in the photo. We ventilate every day and keep the radiators set to levels 2–3. Since today, we have also set up construction dryers. We understand that it takes some time for moisture to leave such an old house.

Lara Julia schrieb:

We are aware that it takes some time for the moisture to leave such an old house.

You’re not really asking anything now.
… so you should understand that you first turn on the construction dryer, then check the humidity as well as the moisture content in the walls, and only then proceed with painting.

ypg schrieb:

You’re not really asking anything now.
… so you should understand that you first turn on the construction dryer, then check the air humidity and wall moisture, and only then paint.

That wasn’t clear to us—no. The stains already improve significantly after just 24 hours with the construction dryer. Thank you!

Finally heats the house and dries it out. As ypg wrote, you cannot paint on damp walls (see the paint manufacturer’s instructions).
You will have to wait and see if the paintwork needs to be redone.