Boletines and certificates
The installation certificate (boletín) legalizes plumbing, gas and electricity: a certified installer signs it and the community, insurer and any sale will ask for it.
When it's needed
New installation, bathroom renovation with routing changes and boiler or heater replacement: each generates its certificate. Without it, the utility can refuse connection and the insurer dispute the claim.
Who issues it
Only an installer certified in the corresponding specialty: the registered plumber issues water and gas; the electrician, electrical. The paper is registered with the relevant body and you keep a copy.
Keep them forever
The home's certificate folder is part of its value: sales and mortgages request them, and disputed claims are settled by them. Scan them and keep them handy — you never know when they're gold.