Common causes are amateur installation of hardware and fixtures, exterior rust damage, or simple failure to call a chimney sweep. Water heaters are seldom in total compliance with code requirements. Violation include inadequate strapping, substandard overflow piping, unsafe flue conditions, and faulty gas lines. Gas furnaces often harbor defects. Given the potential for major consequences, annual servicing by the gas company is recommended.
Faulty firewalls are common in garages.
Violations include, holes, unprotected attic accesses, doors not fire rated, drywall that is too thin, and exposed wood framing. Minor plumbing defects are commonly found, including loose toilets, dripping faucets, slow drains, leaking drains, hot water at the right faucet, and so on. Failed seals are routinely found at dual pane windows, resulting in fogging. This is most common with windows manufacturer during the 1980's. An unabridged list of likely home inspection findings would probably fill a few volumes subject to addenda on a routine basis.