Recharging an expansion tank for your boiler heating system is not difficult but it will require a few tools. This procedure can be done by the savvy homeowner, but it will take some time from start to finish, so allot yourself several hours.
Step 1: Define Expansion Tank Recharge
An expansion tank is attached to your boiler heating system to reduce the event of overflow into a home or other building. It is a pressurized tank. When water takes up too much space in the expansion tank it will cause the air pressure to change. Recharging an expansion tank is the act of basically removing the water to fill the expansion tank with the appropriate amount of water to give the correct pressure again.
Step 2: Inspect the System
Check the fittings in the boiler unit and ensure that you do not have any leaks. Since you already have the boiler down for recharge this is a perfect time to verify the rest of your unit is functioning properly.
Step 3: Drain the Tank
Turn off the boiler switch. Close the pipe valve that connects water flow from the water tank to the expansion tank. Sometimes there will be a hose attached to the expansion tank. If there is not one just attach a standard garden hose. You can also put a bucket under the drain. Open the valve on the tank to expel water. Either loosen or completely remove the six sided fitting, using a pipe wrench or adjustable wrench on each side of the connection. After attaching the garden hose make sure that you have run outside or to an installed drain on the floor to keep the floor dry and safe. Open the valve and completely drain the tank. If you do not drain the tank completely then it will not properly recharge.
Step 4: Recharge Expansion Tank
Once you are sure that there is no more water in the expansion tank remove the hose and close the valve. If you removed or loosened the six sided fitting, re-attach it, or tighten it back up. Turn on the water valve between the water tank and the expansion tank. You will hear water running through the system. When you do not hear water flow in the system any more check the pressure by reading the air pressure gauge. It should show between 10 and 12 psi.
Step 5: Complete the Unit Recharging
When you see that the air pressure is at 10 to 12 psi turn the boiler switch back on. If you find that you cannot maintain the proper air pressure in your system it is possible that you may need to replace the pressure reducing valve, or you may have another problem in the system. Shut off the power to the boiler in this case, and replace the pressure reducing valve. Use the mop or other absorbent cloths to wipe any water up to eliminate slip hazard.