You can test a thermal expansion tank on a water heater by checking the air valve at the bottom of the tank.
Thermal expansion tanks are crucial components in closed water heater systems. As water heats up, it expands. In a closed system (like one with a backflow preventer), this expansion has nowhere to go, leading to excessive pressure that can damage plumbing fixtures, pipes, or even the water heater itself. The expansion tank provides a buffer zone to absorb this extra volume and pressure.
A thermal expansion tank typically has a diaphragm inside, separating a water chamber from an air chamber. The air chamber is pressurized. When hot water expands, it pushes against the diaphragm and enters the water chamber, compressing the air in the air chamber and maintaining a safe pressure level in the system.
How to Test Your Thermal Expansion Tank
Testing your thermal expansion tank is relatively simple and can help you determine if the diaphragm is intact and if the air side holds pressure.
Here's the primary method based on common practice and the provided reference:
Using the Air Valve
The most common and direct test involves the air valve, which looks like a tire valve (a Schrader valve), usually located on the bottom of the tank.
According to the reference, you can tell if your thermal expansion tank is working by pushing the air valve (Schrader valve) on the bottom of the take and seeing whether or not air comes out.
Here's a step-by-step breakdown of this test:
- Locate the Valve: Find the Schrader valve, typically covered by a plastic cap, on the air side of the tank (usually at the bottom or top, depending on the tank's orientation).
- Remove the Cap: Unscrew the plastic cap.
- Briefly Depress the Pin: Use a small tool (like a tire pressure gauge or a tiny screwdriver) to briefly push the pin in the center of the valve.
- Observe the Release:
- Air Comes Out: If air comes out, it indicates the air side of the tank still holds pressure, and the diaphragm is likely intact (at least not fully ruptured allowing water into the air chamber).
- Water Comes Out: If water comes out, it's a strong indication that the diaphragm inside the tank has failed, and the tank needs to be replaced. The water has breached the diaphragm and is now in the air chamber.
- Nothing Comes Out (or very little air): If nothing or very little air comes out, the tank has lost its air charge. While this doesn't necessarily mean the diaphragm is broken, it does mean the tank isn't functioning correctly to absorb pressure. You may need to check the pressure (see below) and potentially recharge it, but often it indicates a slowly failing tank.
Additional Checks
While the valve test gives a good initial indication, a more thorough check involves measuring the air pressure:
- Check Pressure: Using a tire pressure gauge, check the air pressure at the Schrader valve. The pressure should ideally match your home's incoming cold water pressure when the tank is empty (no water on the water side). If the pressure is significantly low or zero, the tank isn't working effectively. You may be able to add air with a pump, but if it loses pressure again quickly, it likely needs replacement.
- Tap Test: Gently tap the top and bottom of the tank with a small hammer or wrench.
- A working tank should sound hollow on the top (air side) and solid or dead on the bottom (water side when the system is pressurized).
- If the tank sounds solid or heavy all over, it's likely waterlogged, meaning the diaphragm has failed or the air charge is lost, and the tank is full of water.
When to Test
It's a good practice to test your thermal expansion tank annually as part of your water heater maintenance routine. Testing quickly can help prevent potential damage to your plumbing system from excessive pressure.
