The first house I bought with my ex husband was a brand new build. We couldn't afford the builders central heating as well so managed for a year with the gas fire in the front room. Neither I or my ex had any plumbing skills.
We got a recommended plumber in to fit central heating later. He had fitted colleagues heating with no trouble. He had expanded the business in the meantime and taken extra staff on. Two "plumbers" came to fit central heating with a back boiler behind a gas fire in the front room. All was completed and worked well untill we had a heavy frost. Woke up to no heating and water pouring across the front room from under the fire. Couldn't get hold of the plumber and we later found he had gone bankrupt.
We had a firm come from town to look at the system. The cowboys had removed the inner cavity wall as the boiler was to big to fit in the gap. The boiler cooled overnight when the heating wasn't on and froze bursting it in the morning when the gas lit. He discovered we had no drain points on the downstairs radiators. There was a shut of valve by the hot water tank that if we had used it would have caused the boiler to explode. He discovered quite a few other faults and ommissions. He asked if he could take photos for his trade magazine to show what cowboys do. It cost nearly as much to have it put right as the original installation did.