Your expansion tank has a single, yet extremely vital purpose. It is created and used to be an over-flow solution for a hot water system. It is a one-way system.
Once the water gets into the expansion tank it does not flow back into main hot water tank. If you have a closed-vent boiler based system, occasionally the expansion tank will need to be drained of water to be recharged for future effective over-flow use.
Step 1 - How to Determine if Expansion Tank is Full
While the boiler is running you can put your hand on the bottom of the tank. If you can feel heat on the bottom of the tank, place you hand at the top of the expansion tank. If it feels cool, then run your hand down from the top of the tank and feel where the temperature of the tank feels warm.
The warm area of the tank is the region in which the water is sitting. If the tank is more than half full of water it is time to purge it. This is important because water does not allow the correct pressure for the boiler to work properly.
Step 2 - Prepare Boiler to Drain Expansion Tank
At least once a year, and sometimes twice a year, the expansion tank should be drained. This will help to keep the air pressure that is necessary for the boiler system to maintain a healthy level keeping your hot water unit working properly.
It is recommended to do the draining before the weather gets too cold, usually early fall and late spring. Turn off the switch for your boiler and shut all the water supply valves. If the boiler system is hot let it cool before working with it.
Step 3 - Drain the Tank
Locate the purge valve that is on the expansion tank. You can also place a five gallon bucket under the valve if you do not have a hose. The tank should drain completely. If it does not expel all the water then the tank will not recharge air pressure properly. If the water stops being eliminated from the tank there could be an air pocket keeping the water from being released.
Many times blowing air back into the expansion tank will pop this air pocket and allow the water to continue flowing. Be aware that once you stop blowing into the hose the water may come out quickly. Once you feel the air pocket is released be prepared to move the hose quickly from your mouth.
Step 4 - When Tank is Empty
When the boiler expansion tank is completely empty the purge valve should be closed, and the supply valve for the water needs to be open. Check all pipes and valves to ensure that they are not leaking from the additional water pressure forcing air out of the expansion tank. Boiler maintenance involves more than an occasional tank purge. If your boiler is 10 years or older then conscious effort should be utilized.