Frozen pipes
A frozen pipe rarely floods a house while it is frozen. The ice plugs the line. The flood arrives on the thaw, often when nobody is home to hear it.
Where they freeze here
Lines run through an unheated crawl space, along an exterior wall in an uninsulated older house, through a garage ceiling, or out to a hose bib that was never shut down for the season. In the pre-war housing common across the Baltimore rowhouse belt, supply lines were frequently run in exterior walls with little or no insulation behind them.
A cold snap combined with a wind driving on one face of the house will freeze a line on that side while the rest of the plumbing is untouched.
Thawing without causing a burst
Open the faucet the frozen line feeds, so melt water has somewhere to go and you can hear when flow returns. Apply gentle heat from the faucet end back toward the frozen section — a hair dryer or a heating pad, never an open flame or a torch.
Heating the middle of an ice plug first traps melt water between two plugs with nowhere to expand, which is precisely how a line splits.
Check the whole run once it flows
A split in copper can be a hairline that only weeps under full pressure. After flow returns, follow the line as far as it is visible and check for weeping at joints and along the length. If the line runs into a wall or ceiling you cannot see, watch that area for the next day.