My Backflow Preventer is Causing Problems With My Hot Water Heater

Hot Water Systems

• Hot water heater systems use a reservoir tank, a heating device and a water supply to deliver heated water throughout a home. Reservoir tanks include insulating materials that help keep heated water supplies hot. A hot water heater requires gas, oil or electricity to power the heating device. As cold water naturally drops to the bottom of the tank, heating devices warm cold water from the bottom while hot water moves up and out from the top of the tank. Cold water supply pipes enter the reservoir tank from the bottom. Air pressure and air temperature controls also appear at the bottom portion of the tank.

Check Valves

• A backflow preventer operates as one of two check valve devices located at the bottom of a hot water heater. A backflow preventer works alongside the valve that feeds water into the tank, also known as the water feeder valve. The backflow valve does pretty much what its name implies -- it prevents tank water from flowing backwards into a home’s main water supply. Since backflow water can potentially contaminate an area’s water supply, some municipalities require all hot water heater systems to have a backflow preventer valve in place. On newer model water heaters, the water supply valve includes a built-in backflow preventer component as opposed to the separate valves found on older model appliances.

Water Pressure Effects

• Both the water feeder and backflow valves respond to water pressure changes in a heater system. Water pressure changes occur whenever water tank levels drop below a certain amount or the main water supply line has a drop in pressure. Tank levels can drop in response to heavy hot water usage within a home. Pressure drops in the main water supply result from vacuum effects caused by activities outside the home. Activities that cause pressure drops include running garden hoses, breaks in the main water line or the use of a nearby water hydrant.

Thermal Expansion

• Since hot water heaters make hot water available on an ongoing basis, heater systems must keep the water warm at all times -- even in cases where little to no hot water is used. This requires heater systems to fire up when water temperatures drop below a certain point. Whenever water heats up, it expands in mass. As a result, water heater tanks may undergo thermal expansion as water temperatures increase.

  Increases in water temperature and mass cause increases in water pressure inside the tank. When this happens, heater systems that have no backflow preventer can discharge excess water into the main water line. Systems that have backflow preventers may see significant damage as tank water overflows into a home plumbing system and water-sourced appliances. Thermal expansion can also damage the water heater system itself. Under these conditions, adding an expansion tank can provide a place for overflow waters to go.