What Factors Can Cause A Backpressure-Backflow Condition?

Back pressure-backflow is created whenever the downstream pressure exceeds the supply pressure which is possible in installations such as heating systems, elevated-tanks, and pressure-producing systems. An example would be a hot water space-heating boiler operating under 15-20 Ibs. pressure coincidental with a reduction of the city water supply below such pressure (or higher in most commercial boilers). As water tends to flow in the direction of least resistance, a backpressure-backflow condition would be created and the contaminated boiler water would flow into the potable water supply.