As said already, in three months any faults should have shown up a long time ago, however I have to be fair found faults years after the event, normally in some ones house who did not even realise some thing was not working, but the problem is to work out who is at fault, very rarely does anyone actually research to find who's fault it was, except with a death. The
Emma Shaw case comes to mind, due to the death the HSE really went to town, and it was not one single person, but a collection of errors.
1) Electrician left a loop of cable.
2) Plasterer put a fastener through the cable.
3) Plumber did not use glue on the tun-dish.
4) The immersion heater thermostat failed.
5) Either there was not a cut out fitted or did not work.
6) Electricians mate fudged up results.
7) Electrical foreman used unskilled labour (see above). (Courts blamed this man)
8) She tried to turn off water before electric in spite of seeing sparks.
Most faults are like above a collection of errors, including poor manufacturers designs, a couple of years ago I was called to father-in-laws house with no domestic hot water, the fault was caused by a change to smart meters, and the guy had failed to re-light the pilot flame on the boiler, however it was summer and he had solar water heating panels, so that should have not in its self caused no hot water, he had turned on the immersion heater as well, so seemed odd, so next was look at immersion heater, only to find it was missing, and the supply to immersion heater was now feeding the pumps for the solar panels, so since not re-labelled he had switched off solar panels, they did not work, but this could be due to over heating due to being switched off, so got a firm in to re-pressurise the system, it still did not work, well not fully not working, it raised the temperature around 10°C but that is really not working, they returned and said the house roof slopped in wrong direction and that was about the best we could expect, house was sold and whole system ripped out by new owners.
However in essence my father-in-law was sold a pup, it would it seems never have worked, but before the family realised this it had been installed around 4 years, the firm had it seems been employed to replace a front door, which they did well, but after that had returned to do a whole list of work, replacing landers with plastic which fell off, and had to be replaced which to be fair they did FOC, they fitted an electric garage door, only access to garage which had the CU inside the garage, with no emergency access release so in a power failure you could open door to replace a fuse, again corrected FOC. And the the solar panels, had my father-in-law not died they may have fixed them, who knows, but as said 4 years before the family found there was a fault.