A backflow preventer is a great component to install on a water heater. They aren't foolproof though, and several things can happen to them. If you are experiencing a problem with your preventer, here are a few things to check:
Step 1 - Check for Poor Water Flow
When a backflow preventer is installed, a water meter and valve are installed on either side. If the water meter isn't getting an accurate reading it can decrease the water flow. This decrease in water flow will mean longer periods of time before you have hot water. Before you replace the preventer entirely, check the water meter.
Step 2 - Look for Leaking Pipes
If you notice a puddle of water near where the backflow preventer was installed, you should look for the valve that controls the water. This valve is essential to keep the water from flowing back. If the valve is loose or faulty the water will have no place to go, and it will puddle on the floor underneath.
Step 3 - Find High Pressure
If the backflow preventer wasn't installed with an expansion tank, the pressure in the water heater can get too high. This can lead to dangerous situations. Most plumbers will recommend installing a thermal expansion tank in conjunction with the backflow preventer to help keep the pressure down.