How to Fix a Leaking Expansion Tank

A man looks at a boiler system.
What You'll Need
Pipe wrench
Teflon tape
Plumbers putty
Garden hose or bucket
Towels, rags, or a mop
Blow dryer
Soapy water

Even in the best boiler system, your expansion tank may begin to experience some leaks. The expansion tank is a pressurized system. The changes in pressure due to overflow from the boiler during water expansion, as well as having moving parts, makes for the potential for degradation of the system.

Step 1 - Investigate to Find Source of Leak

Use rags or a blow dryer to dry the external areas of the expansion tank and make a visual inspection of the surface. If you have trouble finding the origin of a leak in your tank, you can put soapy water around the areas that are wet and watch for air bubbles. Once you have located the leak you can begin work on repairing your boiler expansion tank.

Step 2 - Prepare Expansion Tank for Repairs

Before beginning to work on the expansion tank it is important to shut off the power switch to the boiler system, disconnect any electric plugs, and turn off the gas feed (if you have a gas heated boiler). Turn off the valve that feeds water from the boiler to the expansion tank. Attach a hose to the outlet valve and drain any water out of the expansion tank. You can also drain the water into a bucket if you don't have a hose available.

Step 3 - Repair Expansion Tank

  • Circulator Leak

Remove the intake pipe from the boiler to the circulator. Remove the circulator pump from the unit and replace the gasket. Replace the circulator by putting Teflon tape around the threads and tighten it using two pipe wrenches. Replace the pipe in the same manner, by putting Teflon tape on the threads and tighten with the pipe wrenches.

  • Faulty Pressure Relief Valve

The pressure relief valve can be replaced by shutting off the water feed valve and then removing the pressure relief (reducing) valve in your pressure system. Always use two pipe wrenches to reduce the chance of twisting the pipes and causing cracks in the lines.

  • Leaking Connections on Pipes

If a pipe connection is leaking then the best method to fix the problem is to open up the pipe joints and wipe up any expelled water. Clean the connections with some cleaning agent and a plastic scratcher pad. Be careful using metal to clean a brass or copper line because it is soft metal and you can damage the threads. When the threads and the connection are clean, wrap new plumber's tape around the threads of the male end of the pipe and screw the two pipe ends together.

Step 4 - Recharge the Expansion Tank

After you are sure that you have resolved the leaks, it is time to turn on the valve between the boiler and the expansion tank. You should hear water filling into the expansion tank. Check the pressure gauge. If you see a pressure of 10 to 12 psi then the tank is properly charged. Watch to ensure that the pressure does not change, as that could indicate another leak or a faulty component in your system.