Leak test of water pipes - How long should the pressure remain

Hello,

Yesterday our plumbing installer apparently completed his rough installation. A manometer is attached at the washing machine connection, which showed 2.9 bar last night. Today it was only 2.6 bar. These are Mepla pipes. I assume he performed a pressure test with compressed air. Is it normal that the pressure does not hold for that long?

But the pressure must still hold one or two weeks later. We had a test at five bars, and it was maintained from the laying of the pipes until after the screed was poured and the plumber came again... Definitely keep on it...