Damp

If the paint is peeling off your walls it is most likely to be due to dampness. The best way is to scrape off the affected areas and treat with Fijador which should seal the wall against further dampness. Then you can repaint the walls.

Ventilation is important.. it might seems better to close all the external doors and windows, but any condensation/damp has no where to go... Fitting air-bricks or other ventilation might just solve your problem..

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Blown tiles are another giveaway.

Any tiles in any of the areas mentioned?