To claim for problems arising from the domestic hot water (DHW) system, a technician must examine and assess the defects and issue an expert report confirming the damage, and the claim must still be within time against the installation or construction company or the developer.

Liability for poor installation of the DHW system
There are various problems with poor installation of DHW systems: no access to the interior for cleaning and disinfection (the tank must have a manhole for proper cleaning, to avoid rust or deposits), problems with the temperature regulator, materials not suited to the water pressure, and the addition of chemicals for cleaning and disinfection.
How to claim for a faulty hot water system
If it was installed by the developer or by a company the developer subcontracted, the developer is liable for fault in choosing the contractor (culpa “in eligendo”), that is, for having chosen an unreliable installation company. To bring a claim against those responsible, you should appoint an expert (in court proceedings a court-appointed expert may also be called in) to assess these problems and, on the basis of the expert’s repair proposal and estimate, claim against those responsible.