How to replace a hot water heater expansion tank

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Save money by doing the basic maintenance on your water heater yourself. One of the most important maintenance tasks is replacing the expansion tank. While it may seem like a big job, it's actually quite a simple operation.


Determine the system pressure. Open a tap in the house for 1 to 2 minutes to allow the system pressure to equalize and then close the tap. Read and record the system pressure at the pressure gauge.

Pre-charge the expansion tank by pumping air into it until it reaches the system pressure.

Check the pressure with a tyre pressure gauge.


Turn off power to the water heater system and allow it to cool. This may take up to an hour.

Shut off the water supply to the water heater system. The shutoff may be at the heater itself or it may be further up the pipeline. Turn the valve handle so that it is perpendicular to the pipeline to close it.

Drain the system to reduce water pressure. Check if there is a bleeder valve on either the heater system or near the old expansion tank. Be sure to have a bucket handy to catch the water. Be careful, as it may be pressurized. You may have to drain off air at the radiators themselves to reduce pressure.

Disconnect the old expansion tank. Again, water may leak while you're doing this. Be careful not to damage the piping while you do so.

Put your new tank into place. You may need to install new support brackets for your new tank, or you may be able to use your old brackets if the tanks are the same model.

Wrap Teflon tape around the male ends of your connectors. Avoid the first two threads, as tape put here will end up in the system. Teflon paste, in addition to tape, will give you extra sealing.

Connect the system to the new expansion tank. Be sure to screw the connectors in tight, but do not strip the threads doing so.

Turn on your water pressure. Examine your connections to make sure water is not leaking.

Open a hot water tap to run water through the system. Again, check your connections to make sure no water is leaking.

Turn on the hot water heater and allow it to heat up. Once it does, check to make sure you're getting hot water.

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