How to Replace a Water Heater Expansion Tank

A water heater.
  • 3-5 hours
  • Advanced
  • 400-600
What You'll Need
Tire pressure gauge
Tape (Teflon)
Wrenches (dependent on pipe/bolt types)
Expansion tank

For the sake of safety, you may need to know how to replace a hot water heater expansion tank. The expansion tank is a crucial aspect of plumbing in regards to the water heater. Where there is heat, there is expansion. So, as the water heats, the pressure increases, which could lead to water that is too hot, which could be a safety hazard and cause other plumbing problems. It could lead to leaking pipes, as they are not used to, or meant for, such pressure and temperatures.

Step 1 - Prep

The first step before actually getting in there and replacing the tank is to determine the system pressure. To do this, open a faucet anywhere in the house structure for one to two minutes. During this time, the system pressure will equalize itself. Then, close the faucet, and read and record the system pressure at the pressure gauge. Next, pre-charge the water expansion tank by pumping air into the tank until it reaches the system pressure—the two readings should match by checking it with a tire pressure gauge.

Step 2 - Get Started

Turn off the power to the water heater system and wait at least one full hour for the water throughout the plumbing structure to cool. Afterwards, shut off the water supply to the water heater itself by turning the valve handle until it is perpendicular to its pipeline. Drain the system, which will reduce pressure. Next, note where there may be “bleeding” pipes, and use the buckets accordingly to catch any dripping water. Be careful, as the water may be pressurized and air may be needed to be drained off at the radiators to further reduce pressure. Disconnect the tank you are replacing while not damaging the surrounding piping.

Step 3 - Install

Installing your new tank may require new support brackets if the model is different than the older one. Otherwise, the old brackets should work fine. Next, wrap Teflon tape around the male ends of the connectors, but not within the first two threads. Screw the connectors tight, but do not strip anything when using your wrench.

Step 4 - Test

Testing a new water expansion tank is a little complex, so be patient. First, turn the water pressure back on and note any leaks. When leaks do exist, fix accordingly; problems may arise from the pipes, the brackets, or the connectors. If or when there are no leaks in the plumbing, continue to open a faucet for hot water. Again, note any leaking pipes and fix them accordingly.

Check your connectors to ensure there is no water leaking out. If or when there are no leaks, turn the water heater on and allow the water to heat up. Again, note any leaks. Also, check to see that the new flowing water is hot. Because of how complex the testing is, you may need to call a professional plumber to double-check that everything is working smoothly, or if it isn't, to see what the problem may be if you cannot figure it out.